Kano, Nigeria (CNN) -- Heavily armed men descended on the school as the girls slept.
Bullets flew as guards fought back, but they lost.
The men, Boko Haram militants, herded more than 100 students onto buses, vans and trucks and drove off, flanked by motorcycles, authorities said.
That was Monday. By Wednesday, just eight of the 129 abducted school girls were still missing, according to the Nigerian military.
It was not immediately clear how the girls became free. Their conditions were also not clear.
"They forced us into trucks, buses and vans, some of which were carrying foodstuffs and petrol. They left with us in a convoy into the bush," said a student among the girls who escaped and who declined to be named for security reasons. "A group of motorcyclists flanked the convoy to ensure none of us escaped."
At one point, one of the trucks broke down and the girls on that vehicle were transferred to another one, the student said. The broken down truck was set on fire, she added.
When another vehicle broke down and the men tried to fix it, "some of us jumped out of the vehicles and ran into the bush. We later found our way back to Chibok," she said, referring to the northeastern town where her school is located.
One of the alleged attackers has been captured, and a military search-and-rescue operation is ongoing to "ensure the safety of the remaining students," Maj. Gen. Chris Olukolade said Wednesday.
Boko Haram, which translates as "Western education is sin," is an Islamist militant group waging a campaign of violence in northeastern Nigeria, particularly in the states of Borno, Yobe and Adamawa.
The group is known to have carried out deadly attacks on other schools in the northeast. In a clip released by the group on March 23, leader Abubakar Shekau threatened to launch raids and abduct girls from schools.
"They took away my daughter and my niece ... and we fear for their safety in the hands of these merciless people that take delight in killing and destruction," said the mother of one of the abducted girls. "I don't know what to do. The whole family is confused and we have turned to prayers, which is all we have."
In early March, Borno state's government closed all its 85 secondary schools and sent more than 120,000 students home after increasing Boko Haram attacks.
The Nigerian government is struggling to control the bloodshed between the mainly Muslim north and Christian south that has claimed more than 3,000 lives since Boko Haram came to prominence in 2009, according to Human Rights Watch.
Rescue teams are fanning out in the forest
Rescue teams, aided by surveillance helicopters, were moving deeper into the vast forest that extends into neighboring Cameroon and other states in the region, said Ali Ndume, a senator representing southern Borno state, in which Chibok is located.
"Soldiers and the Civilian Joint Task Force, as well as volunteers from the area, are now combing the forest to rescue the schoolgirls. They are aided by surveillance helicopters to locate the kidnappers' position," Ndume said.
The teams ventured into the woods after a broken down truck believed to have been part of the kidnapping convoy was found abandoned at the edge of the forest, which suggests that the abductors took their hostages into the woods on foot, he added.
A military official involved in the rescue operation also confirmed a broken down truck was found in the brush.
"We are now trying to locate the whereabouts of the abducted girls," said the military source, who asked not to be named because he was not authorized to speak on the issue.
Before the military's announcement that most of the students had been freed, Borno Gov. Kashim Shettima told reporters about 14 girls had escaped. He pledged 50 million naira, around $300,000, to any person or persons who could provide information that would lead to the rescue of the girls.
'Pain, sorrow and anguish' for families
Distraught parents of the abducted girls anxiously waited for news, many of them crowded outside the burned home of the Chibok district administrator.
The gunmen burned homes and businesses in the town as they fled with the girls, witnesses said.
"We are calling on the government to do everything possible to track these people and save your daughters from them. They should not allow our daughters' dreams to be shattered by these murderers," said the mother of one abducted girl.
A statement from the office of Nigerian President Goodluck Jonathan, said he ordered security forces "to deploy maximum efforts" in rescuing the girls and welcomed reports of some rescues.
"President Jonathan deeply regrets the pain, sorrow and anguish brought upon many Nigerian families in recent days as a consequence of recurring security challenges which the nation is contending with," the statement said.
U.N. Secretary-General Ban Ki-moon called for the girls' "immediate release," according to a statement from Ban's spokesperson. He is "deeply alarmed about the increasing frequency and brutality of attacks" against schools in northern Nigeria.
"The targeting of schools and schoolchildren is a grave violation of international humanitarian law. Schools are, and must remain, safe places where children can learn and grow in peace," the statement said.
CNN's Vladimir Duthiers contributed to this report.