STORY HIGHLIGHTS
- Aleppo, Syria's largest city, is rife with violence and a focal point in Syria's civil war
- Families packed onto motorcycles and into cars Sunday, trying to flee to safety
- An unknown number of people are trapped in their homes, a U.N. official says
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Northern Syria (CNN) -- They packed one on top of another -- children, parents, grandparents -- onto motorcycles, as many as six at a time, and then sped away as fast as they could. Others clambered into cars, as gunfire crackled around them.
There was no time to wait, with violence engulfing their home city of Aleppo.
These families were not alone. Amid intensifying shelling and heavy weapon fire in Syria's most populated city, a U.N. official -- citing the International Committee of the Red Cross and the Syrian Arab Red Crescent -- said that about 200,000 people have fled Aleppo over the past two days.
Fighting rages in Aleppo

Rebel fighters load an anti-aircraft machine gun on an armored vehicle in Atareb, east of Syria's second-largest city, Aleppo, on Tuesday, July 31. Unrest spread across other volatile regions of the country as forces of President Bashar al-Assad's regime shelled targets and launched raids in and around Damascus, Homs, Daraa and Deir Ezzor.
Syrian boys run near a building hit by bullets and fire in Atareb.
A member of the Free Syrian Army fires at forces loyal to President Bashar Al-Assad in a district of Aleppo called Salah Edinne on Tuesday.
A member of the Free Syrian Army carries an injured civilian to safety in Aleppo's district of Salah Edinne on Tuesday.
Members of the Free Syrian Army learn that a tank belonging to forces loyal to President Bashar Al-Assad is heading to the area.
A Syrian boy carries bags of bread as people wait outside a bakery near Syria's second-largest city, Aleppo.
A photo released by Syrian Arab News Agency depicts damaged buildings in Homs on Monday, July 30.
A Free Syrian Army fighter takes position Sunday, July 29, in Aleppo as people flee shelling. Intense clashes have been under way for more than a week between the regime and rebels in Aleppo, Syria's commercial and cultural center.
Parts of Syria's largest city saw the fiercest clashes yet in the country's 16-month crisis on Saturday, July 28. About 200,000 people have fled fighting in Aleppo and surrounding areas in the past two days, a U.N. official says.
Fighting leaves vehicles damaged Saturday in the southwestern city of Daraa.
Syrians carry the body of a man allegedly killed in the bombardment of Sukari, southwest of Aleppo, by Syrian regime forces on July 27.
Destruction appears widespread in Homs on Friday, July 27, in a handout photo from the Syrian opposition Shaam News Network.
A Syrian opposition fighter takes aim during clashes with forces loyal to President Bashar al-Assad in Aleppo on Wednesday, July 25.
Family and friends mourn over the body of Usame Mircan, who they say was killed by a Syrian government sniper in Aleppo on Wednesday.
Usame Mircan's mother grieves after he was killed during fighting in Aleppo.
The bodies of men killed during clashes between Syrian rebel fighters and goverment forces lie on the Aleppo street on Thursday, July 26.
Fighters from the Syrian opposition rest at a former primary school in Aleppo on Wednesday.
Residents take cover as fighters from the Syrian opposition clash with forces loyal to President Bashar al-Assad in Aleppo on Wednesday.
Syrian rebels guard a checkpoint in Aleppo on Wednesday.
A damaged portrait of President Bashar al-Assad sits among piles of debris at a checkpoint manned by Syrian rebels in Aleppo on Wednesday.
Syrian rebels drive through Selehattin near Aleppo during clashes with government forces on Monday, July 23.
A Syrian rebel runs through the streets of Selehattin during an attack on a municipal building. The rebel Free Syrian Army says it is attempting to "liberate" several districts of Aleppo.
Syrian rebels work to find snipers during clashes Monday between the opposition and government forces in Selehattin.
Syrian rebels make their way down a street Monday in Selehattin near Aleppo. If they gain control of Aleppo, it would mark a pivotal point in the Syrian crisis.
Syrian rebels take cover behind sandbags during fighting Monday at the entrance to the city of Selehattin.
On Sunday, July 22, a Syrian refugee looks out from a bus as he arrives at a refugee camp in Turkey opposite the Syrian commercial crossing point Bab al-Hawa.
Syrian refugees flee from a refugee camp nicknamed "Container City" on the Turkish-Syrian border in Kilis province, southern Turkey, on Sunday.
A mortar shell falls toward the Syrian village of Jbatha Al-khashab, about 45 kilometers (28 miles) south of Damascus. It's seen from the Israeli side of the border, in the Golan Heights.
Smoke from artillery shelling rises above Jbatha Al-khashab.
An armed Syrian rebel wearing the jersey of FC Barcelona rests with comrades near the northern city of Aleppo on Sunday. The rebel Free Syrian Army announced the start of the battle to "liberate" Aleppo, Syria's commercial hub and a traditional bastion of President Bashar al-Assad's regime.
A Free Syrian Army soldier rips a portrait of President Bashar al-Assad at the Bab Al-Salam border crossing to Turkey on Sunday.
Dozens of Turkish truck drivers on Saturday, July 21, accused Free Syrian Army rebels of having burned and looted their lorries as they captured Syria's Bab al-Hawa post, near Aleppo, from government troops.
In this photo released by the Shaam News Network, a truck burns after shelling in the Erbeen suburb of Damascus on Saturday, July 21.
Refugees fleeing the violence in Syria arrive by bus in Baghdad, Iraq, on Saturday.
Turkish soldiers stand guard at the Cilvegozu border gate in Reyhanly that connects to Syria's Bab al-Hawa post. An estimated 120,000 people have fled Syria to Turkey, Iraq, Lebanon and Jordan.
Burned-out trucks at the Bab al-Hawa Syrian border post with Turkey on Friday, July 20. Syrian rebels seized control of the post after a fierce battle with Syrian troops, an AFP photographer at the scene reported.
Syrian soldiers celebrate in the al-Midan area in Damascus on Friday. Syrian regime forces routed rebel fighters from the Damascus neighbourhood of Midan, Syrian state television reported, saying troops had "cleaned" the district of "terrorists."
Journalists are shown a dead body on a government tour of the al-Midan area in Damascus on Friday.
Members of Syria security forces rest in the al-Midan area in Damascus on Friday.
Syrian army soldiers hang their national flag in a partially destroyed neighborhood in the al-Midan area in Damascus.
Smoke hangs in the air in a partially destroyed neighborhood in the al-Midan area in Damascus.
Members of Syria security forces pose for photographers in the al-Midan area in Damascus after driving out the rebel fighters.
Syrian residents take goods from a truck that rebels captured at the Bab al-Hawa border crossing with Turkey on Friday.
A picture released by the official Syrian Arab News Agency on July 19 shows Syrian General Fahd al-Freij meeting with President Bashar al-Assad in Damascus after his swearing-in ceremony as defense minister.
A man holds up a picture of President Bashar al-Assad at a former police station in Atareb after clashes between Syrian soldiers and Free Syrain Army near Aleppo on Thursday, July 19. Rebels seized control of border crossings with Iraq on Thursday, dealing a new blow to al-Assad, as China and Russia dismayed the West by blocking U.N. action against his regime.
People walk along the street in Atareb amidst damage caused by clashed between Syrian soldiers and the Free Syrian Army.
A Syrian man checks the former police station of Syrian regime after a clash at Atareb on Thursday.
Smoke ascends from from alleged shelling of the Syrian village of Jebata al-Khashab as seen from the hill village of Buqaata in the Israeli-annexed Golan Heights on Thursday.
The death toll in Syria on July 12 reached 287, making it the bloodiest day in Syria since the uprising began. As it has done consistently, Syrian state television blamed "armed terrorist groups" for the killings.
A Syrian woman sits with her grandson outside a damaged building after attacks in the Syrian village of Treimsa on July 13, 2012. More than 200 people were massacred in the town, according to activists.
A Syrian demonstrator holds an opposition flag during a protest in Damascus on July 2, 2012. There have been increasing reports of violence in the Syrian capital.
Syria's President Bashar al-Assad waves as he arrives for a speech to Syria's parliament in Damascus on June 3, 2012. The embattled president denied that government forces were behind the "outrageous" massacre in Houla.
People gather at a mass burial on May 26, 2012 for victims reportedly killed during an artillery barrage from Syrian forces in Houla. The attack left at least 108 people dead, including nearly 50 children, according to the United Nations.
Members of the Free Syrian Army return to Qusayr on May 12, 2012 after an attack on Syrian regime forces in the village of Nizareer, near the Lebanese border in Homs.
A U.N. observer speaks with Syrian rebels and civilians in the village of Azzara on May 4, 2012, days before the country's parlianemtary polls were held against a backdrop of unrest.
Thousands of Syrians wave their national flag and hold portraits of President Bashar al-Assad and Lebanon's Hezbollah chief Hassan Nasrallah, right, during a rally to show support for their leader on March 29, 2012 in Damascus.
Syrian rebel fighters man a checkpoint leading into the town of Taftanaz in the rebel stronghold province of Idlib on March 20, 2012.
A Free Syrian Army rebel mounts his steed in the Al-Shatouria village near the Turkish border in northwestern Syria on March 16, 2012, a year after the uprising began. The Free Syrian Army is an armed opposition group made up largely of military defectors.
Syrian refugees walk across a field before crossing into Turkey on March 14, 2012. International mediator Kofi Annan called for an immediate halt to the killing of civilians in Syria as he arrived in Turkey for talks on the crisis.
A day after the twin suicide bombings, Syrian mourners pray over the coffins of the 44 people killed during a mass funeral in Damascus.
A Syrian man who was wounded in a suicide attack rests at a hospital in Damascus on December 23, 2011. Suicide bombers hit two security service bases in the Syrian capital, killing dozens of people.
Arab foreign ministers attend an emergency meeting at the Arab League headquarters in Cairo on October 16, 2011, to discuss the crisis in Syria.
U.S. Secretary of State Hillary Clinton speaks to the media in Washington on August 18, 2011. Clinton said U.S. sanctions on Syrian oil "strike at the heart of the Syrian regime."
Syrian youths wave national flags while army troops drive out of Daraa on May 5, 2011. During a week-long military lockdown of the town, dozens of people were reportedly killed in what activists described as "indiscriminate" shelling on the city.
Syrians in Damascus protest in the street on March 25, 2011, after clashes with government forces in Daraa left several dead.
Supporters of Syrian President Bashar al-Assad rally on April 1 in Istanbul, Turkey, as delegates from dozens of countries gather to push for ways to end the deadly violence in Syria. The United Nations estimates more than 10,000 people have been killed since the beginning of the crisis in March 2011. The conflict is now being labeled a civil war by the International Committee of the Red Cross.
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Photos: Showdown in Syria
Fighting on the outskirts of Aleppo
Syria prisoner exchange
Syria rebels: We took police station
Some went to neighboring towns and villages they hoped would be safe, while others successfully made the 55-kilometer (35-mile) trek north across the Turkish border.
But not everyone has been able to get away. Valerie Amos, the U.N.'s under-secretary-general for humanitarian affairs, said Sunday in a statement that some residents had huddled in schools and other public buildings trying to find some safety amid the carnage. Basic necessities -- like mattresses, hygiene items, food and drinking water -- are in perilously short supply, she added.
"It is not known how many people remain trapped in places where fighting continues today," Amos said.
Not long ago, Aleppo was busy as Syria's commercial and cultural hub. The northern Syrian city has seen considerable death and destruction over the past few months, after popular anti-government protests spurred a bloody crackdown by President Bashar al-Assad's forces and, eventually, a civil war with organized fighting forces on both sides. Still, the violence wasn't always on the level of places like Homs and the Damascus suburbs.
Historic Aleppo torn apart by war -- again
In the past week, Aleppo has become a major focal point in the war. After taking over surrounding towns and villages, rebel fighters have pushed to try to control the city itself. They've had some success, managing to secure key locations and even set up checkpoints.
An eerie, relative calm prevailed in pockets of the city on Sunday. Families gathered on balconies, while children walked the streets as if nothing had happened.
But that was hardly the case elsewhere in Aleppo, parts of which appeared largely devoid of civilians. Rockets and mortar shells had fallen and continued to fall in many residential areas, while Syrian troops defending a military base located just north of the city fired into neighborhoods.
Concerned about innocent civilians getting caught up in the violence, Arab League chief Nabil Elaraby said Sunday that he believed war crimes were being committed in Aleppo.
Abo Hamdi, an activist, said government forces, tanks and heavy machinery have tried to overrun the neighborhood of Salahuddin, but by Sunday night they were on the outside looking in. He said that opposition Free Syrian Army fighters have brought in ammunition and taken positions around the neighborhood, though government forces with tanks and heavy artillery were stationed nearby.
"The situation in the city of Aleppo is very critical and quite serious," he said. "We are trapped in this neighborhood, but the ... Free Syrian Army is preparing for fierce battle."
Syrian rebels seize military base outside Aleppo
Local diplomacy wins in tense Syria prisoner exchange
CNN's Ivan Watson and journalist Shiyar Sayed Mohamad reported from northern Syria.