(CNN) -- A man dressed in all black fired shots Monday inside the U.S. Navy Yard, injuring several people, according to the Navy and a Washington police spokesman.
The incident began about 8:20 a.m. ET when several shots were fired inside the Naval Sea Systems Command headquarters in the southeast portion of the capital.
The injured included a Washington, D.C., police officer who has been hospitalized, and another law officer not affiliated with the city force, a police spokesman said.
1:07 p.m. ET -- "We have no information to believe that either of those folks are military personnel, but we do have information that those individuals are wearing military-style clothing," Washington Police Chief Cathy Lanier says.
1:04 p.m. ET -- Police are still looking for a white man and a black man in military-style clothing, according to Washington Police Chief Cathy Lanier.
12:57 p.m. ET -- The president says to remember the victims as the investigation unfolds: "President Obama: "We send our thoughts and prayers to all at the Navy Yard who've been touched by this tragedy." #NavyYardShooting," the White House tweets.
12:50 p.m. ET -- President Obama says the country will stand with the victims' families.
12:48 p.m. ET -- Police have released another description of a suspect in the shooting: "Navy Yd Suspects B/M 50 yrs, w/rifle, drab olive military uniform; S2 W/M pistol, Navy-style khaki uniform, short slv,beret call 7279099."
12:46 p.m. ET -- President Barack Obama lamented that the U.S. is "confronting another mass shooting" and called for a seamless investigation involving federal agencies and the military.
12:41 p.m. ET -- Washington police have tweeted a reminder to family members concerned about their loved ones: "Navy Yard Update: for info on family members call 202 433 6151. If you have any info on suspects or were a witness call 202 727 9099."
12:40 p.m. ET -- Obama vows the people responsible for the shooting will be held accountable, as the White House tweets this: "These are men & women were going to work, doing their job, protecting all of us." —President Obama on the victims of the #NavyYardShooting."
12:39 p.m. ET -- President Obama describes the Navy Yard shooting as a "cowardly" act "that targeted military and civilian personnel." He also notes that several people have been shot, some of them fatally.
12:36 p.m. ET -- Public schools will remain on lockdown for now: "We are continuing to work closely with MPD. When MPD advises that #navyyardshooting is resolved, we will lift the school lockdown," the DC Public Schools Twitter account said.
12:30 p.m ET -- A man in his 60s who arrived at George Washington University Hospital with a gunshot wound to his left temple was pronounced dead upon arrival, said hospital spokeswoman Jen Rizzo.
More patients are arriving, she said, and the hospital can handle four or five more critically injured patients and 20 with noncritical injuries. It's not clear how many more are coming, she said.
12:22 p.m. ET -- Washington Police Chief Cathy Lanier also confirms an earlier report of "multiple" fatalities.
12:21 p.m. ET -- There are "potentially" two other shooters being sought in connection with the Navy Yard shootings, Washington Police Chief Cathy Lanier says, confirming one suspect is dead inside Building 197.
12:19 p.m. ET -- An update, via Twitter, from Pentagon press secretary George Little: "#SecDef is receiving regular updates on the tragic situation at the DC Navy Yard. Saddened to hear reports of fatalities and injuries."
12:16 p.m. ET -- The Pentagon Force Protection Agency has "increased its security posture, not out of a specific threat, but as a proactive, precautionary measure related to the ongoing incident at the Navy Yard."
This means more officers at Pentagon entrances armed with automatic weapons, according to Lt. Col. Tom Crosson, a Pentagon spokesman. The Department of Defense has also halted its shuttle services between the Pentagon, the Navy Yard and nearby Joint Base Anacostia-Bolling.
11:58 a.m. ET -- Paul Williams, who works at a nearby nonprofit, was headed to his office when he witnessed panic at the Navy Yard.
"I had my headphones in, so I didn't know what was going on," Williams, 29, told CNN. "I was listening to music, but I heard four rapid bangs -- bang, bang, bang, bang."
At first, he thought it was construction noise -- something common in the area -- but less than a minute later, he saw what he estimated to be hundreds of people coming toward him.
"I didn't know what was happening. I just ran with them," Williams said, adding, "Everyone seemed scared. People were crying. People were being consoled and calling loved ones and family."
11:53 a.m. ET -- One suspected shooter is dead, a senior Navy official tells CNN.
11:51 a.m. ET -- Via Twitter, the Navy has issued two phone numbers for family members looking for loved ones: "Family members looking for information about their loved ones can call 202-433-6151 or 202-433-9713. #NavyYardShooting"
11:48 a.m. ET -- Navy Secretary Ray Mabus has issued two remarks via Twitter: "I'm deeply shocked & saddened by the shooting this morning at the Navy Yard. Our thoughts & prayers are with the victims and their families." And later: "I have complete confidence in our first responders, and I continue to be completely focused on this very difficult situation."
11:46 a.m. ET -- A man and two women were admitted to MedStar Washington Hospital Center with "severe injuries" from multiple gunshot wounds, said chief medical officer Janis Orlowski, adding that the injuries do not appear to be life-threatening.
11:42 a.m. ET -- As authorities work to clear Building 197, where the shootings happened, to ensure there are no additional shooters, Naval District Washington spokesman Ed Zeigler says that the two injured police officers are not among the fatalities reported earlier.
11:37 a.m. ET -- The top Navy officer, Adm. Jonathan Greenart, tells CNN he was evacuated from his residence at the Navy Yard when the shooting began.
11:36 a.m. ET -- "Multiple" people have been killed in the shooting, Naval District Washington spokesman Ed Zeigler says.
11:34 a.m. ET -- Two suspected shooters "are down" at the Washington Navy Yard, Zeigler says.
11:31 a.m. ET -- Helicopters are hovering over the scene, and it appears one chopper contains a police sniper.
11:18 a.m. ET -- The Bureau of Alcohol, Tobacco, Firearms and Explosives is dispatching a special response team similar to the one used to take the Boston Marathon bomber into custody, said law enforcement official Even Perez.
About 20 specially trained agents, accompanied by an armored vehicle, will work with local authorities when they arrive on the scene. ATF agents are already on the perimeter, engaged in the investigation, the ATF says.
11:12 a.m. ET -- Pentagon spokesman George Little says he believes "there has been loss of life," but he would not say how many people are believed dead.
11:07 a.m. ET -- Via Twitter, local police have issued a statement for those concerned about their loved ones: "Navy Yard: family members may reunite at Nationals Stadium Parking Lot B, South Capitol & K St SE."
11:05 a.m. ET -- Heavily armed SWAT officers were seen escorting people from the building where shots were fired.
10:58 a.m. ET -- Two witnesses tell CNN affiliate WJLA they heard their building's fire alarm go off and saw a man with a rifle as they left the building.
"He aimed the gun and fired our way," Todd Brundidge told the station. "I couldn't believe it."
People frantically tried to escape the building, he said. "They were pushing. They were shoving. People were falling down."
10:51 a.m. ET -- At least six Washington-area schools are on lockdown after the shooting, the public school system tweeted.
10:50 a.m. ET -- In addition to the injured Washington, D.C., officer, a base security guard was also injured, said Metropolitan Police Department spokeswoman Saray Leon.
10:48 a.m. ET -- About 3,000 people work at the Naval Sea Systems Command's headquarters, the Navy says.
10:46 a.m. ET -- At least 10 people have been injured in the shooting, according to police, and the U.S. Navy has issued a statement saying there are "several injuries with reports of fatalities."
10:43 a.m. ET -- The suspect in the shooting is a 6-foot tall, bald male of medium complexion, wearing a black shirt and jeans, said D.C. Metropolitan Police spokesman Chris Kelly.
10:40 a.m. ET -- Counterterrorism officials have briefed President Barack Obama "several times" about the shooting, a White House official says.