Officials have confirmed that at least 13 people are dead.
4:21 p.m.: At a press conference just now, D.C. Mayor Vincent Gray updated the death count to 13. That number includes the shooter.
3:34 p.m.: The D.C. Department of Transportation has posted an updated list of road closures around the Navy Yard. Below is the map of said closures:
3:26 p.m.: The New York Times has confirmed the identity of the deceased shooter:
Senior law enforcement officials identified the gunman as Aaron Alexis, 34. A senior law enforcement official said the authorities had identified the dead gunman through his fingerprints.
Three weapons were found on the gunman: an AR-15 assault rifle, a shotgun and a semiautomatic pistol, the official said.
3:17 p.m.: While Navy Yard employees are now being allowed to leave, the Senate locked down at 3:06 p.m., according to POLITICO's Mike Allen. Reports AP: "Senate officials say Senate to be shut down while Navy Yard shooter is sought."
Senate complex locked down at 3:06 p.m.: "You may move about the building...for the next two hours you may not leave nor can anyone enter"— Mike Allen (@mikeallen) September 16, 2013
3:14 p.m.: Annnnd tonight's Nationals game will be postponed, according to the team's PR Twitter account:
Tonite’s #Nationals-Braves game has been postponed and will be made up as split doubleheader (1:05 p/7:05p) on Tue., Sept. 17.— Nationals PR (@NationalsPR) September 16, 2013
3:02 p.m.: D.C. police have ruled out a white male dressed in khaki as a suspect:
The white male in the tan outfit has been identified and is not a suspect or person of interest.— DC Police Department (@DCPoliceDept) September 16, 2013
2:50 p.m.: An increasing number of prominent D.C. personalities--Christine Brennan of USA Today, Washington City Paper Editor Mike Madden, and the Washington Post's Joe Heim among them--are calling on the Washington Nationals to postpone tonight's game against the Atlanta Braves, currently scheduled for 7:05 p.m.
If the Nationals have any sense, they will postpone tonight's game. (For non-DC folks, stadium is just blocks from the Navy yard.)— Joe Heim (@JoeHeim) September 16, 2013
2:39 p.m.: A picture from earlier today of Navy Yard employees on lockdown in the Navy Yard food court:
Watching the news at the Navy Yard food court. Still locked down. pic.twitter.com/B2PIPcWDqJ— Gerritt (@Gerritt) September 16, 2013
2:37 p.m.: D.C. police are asking residents to report information about persons of interest (described by D.C. Police Chief Cathy Lanier in our 2:07 p.m. update) to the following number:
2:14 p.m.: POLITICO reports that the Senate has adjourned until tomorrow.
Reid adjourns Senate until 10 a.m. Tuesday in wake of Navy Yard shooting, postpones judge votes— Burgess Everett (@burgessev) September 16, 2013
2:07 p.m.: D.C. Police Chief Cathy Lanier says "12 confirmed dead at this point." Praises area law enforcement for "heroic" response to today's shooting. "We are now officially transitioning to an FBI lead," meaning FBI will be leading the investigation. Two additional people to be on the lookout for: A white male between 30-40 years of age, wearing a tan military uniform and beret-style hat; a black male between 40-50, wearing olive drab, "graying sideburns." MPD is asking people "to remain in their homes" as the hunt for two additional suspects continues.
Lanier says there are "multiple pieces of information" indicating that two additional people were carrying firearms. MPD has reason to believe they were involved in the shooting in some way.
The search of the buildings could continue for several more hours.
2:06 p.m.: D.C. Mayor Vince Gray updates the press for the second time today. Says there's no known motive for the shooting.
2:02 p.m.: Unsurprisingly, today's shooting will have ramifications for D.C.s public transportation through the afternoon. The Washington Post: "Metro transit officials said the 92, 96, 90 and V7 bus routes have been impacted since the incident at Navy Yard began this morning and are likely to face delays throughout the afternoon due to street closures in the area. Metrorail has not been impacted by the situation."
1:49 p.m. D.C.'s MLB team, the Nationals, has been granted access to the stadium for practice. (The stadium is near the Navy Yard.) Tonight's game, if it actually happens, is at 7:05 p.m. NBC4's Tom Sherwood tweets, "NATS game - 35k fans, 100s of ballpark workers -- still on as of this moment. no announcement."
1:31 p.m.: The most chilling anecdote from today's shooting comes from Navy Commander Tim Jirus, who told reporters just minutes ago that a man who approached him to alert him to the presence of a shooter was shot through the head as he was talking. Jirus says he immediately ran for cover.
1:12 p.m.: The AP has released a video interview with a witness of the Navy Yard shooting:
1:07 p.m.: The deceased gunman has still not been identified. NBC reports that the possibility of a second and/or third shooter is "fading."
12:32 p.m.: President Obama: "We are confronting yet another mass shooting." Employees at Naval center "know the dangers of serving abroad, but today they faced unimaginable violence... here at home." After promising to do whatever necessary to bring shooter(s) to justice, Obama remarks on Syria, and then, five-year anniversary of the financial crisis.
12:28 p.m. CBS claims to have more info on the deceased shooter:
BREAKING. Source tells CBS's Stephanie Lambidakis shooter was civilian Navy employee who had "some kind of job issue" earlier this year.— Charlie Kaye (@CharlieKayeCBS) September 16, 2013
12:27 p.m.: GW Hospital presser: The first gunshot victim the hospital received died within a minute of arriving at the hospital. He was in his 60s and had an "unsurvivable wound" in his left temple. He was the first victim to be transported out of the Navy Yard. (Via The Atlantic's Tom Kelly, on the scene at GW Hospital.)
12:19 p.m.: NBC's Pete Williams says that the black shooter described by D.C. Police Chief Cathy Lanier matches the description of the confirmed deceased shooter.
12:13 p.m.: D.C. Police Chief Cathy Lanier: D.C. police sent multiple active shooter teams to Navy Yard. One MPD officer was shot. One shooter is deceased. The "big concern" for Lanier is that there are potentially two other shooters "out there": a "white male" last seen around 8:35 a.m., wearing a khaki tan military uniform and a beret hat, carrying a handgun. Also another possible shooter: around 50 years of age, black, wearing an olive drab military style uniform and carrying a long gun.
12:12 p.m. D.C. Mayor Vince Gray speaks to the press about the Navy Yard shooting.
12:11 p.m.: Yahoo! reports new details on the alleged shooter.
BREAKING UPDATE: One gunman in DC Navy Yard shooting is dead; man in his 50s, former Navy official, employment status unknown @ABC— Yahoo News (@YahooNews) September 16, 2013
12:06 p.m.: Reporters wait for D.C. Police Chief Cathy Lanier
12:05 p.m.: AP reporting six people dead.
BREAKING: Navy officials say at least 6 dead in Navy Yard shooting.— The Associated Press (@AP) September 16, 2013
D.C. Public Charter School Board says five schools and one school administrative building, all near #NavyYard, are still on lockdown.— City Paper (@wcp) September 16, 2013
11:48 a.m.: MPD Chief Cathy Lanier will be speaking to the press shortly after noon, an MPD spox just told reporters staged for a press conference. The spox also dismissed reports that there is an active shooter situation at Joint Base Anacostia-Bolling Air Force Base.
11:47 a.m. AP: "At least one gunman was killed about 10:30 a.m. EDT after opening fire inside the Naval Sea Systems Command headquarters, where about 3,000 people work just miles from the Capitol."
11:44 a.m. Multiple news outlets are reporting that the Navy Yard shooter is dead. No word about a second shooter.
Family members looking for information about their loved ones can call 202-433-6151 or 202-433-9713. #NavyYardShooting— U.S. Navy (@USNavy) September 16, 2013
11:41 a.m. Washington Hospital Center has been told to expect more gunshot victims from the Navy Yard.
11:38 a.m. A picture of officers encircling a Navy Yard building.
11:35 a.m. A visibly distraught representative of Washington Hospital Center is giving a press conference. The hospital is treating one police officer and two civilian victims. All three are in critical condition. A male patient has gunshot wounds to both legs, a female patient was shot in the shoulder, and a third female victim has gunshot wounds to the head and the hand. All three have good chances of survival.
11:31 a.m. The view from where journalists have gathered for a police press conference. VIa NBC4's live feed.
11:29 a.m.: One shooter is allegedly dead.
11:26 a.m.: NBC reports that law enforcement are clearing a second building; and that at least one shooter was carrying an AR-15, a shotgun, and a handgun.
Tactical teams have entered second building at D.C. Navy Yard - @PeteWilliamsNBC— NBC News (@NBCNews) September 16, 2013
11:15 a.m. Per usual with breaking news stories, there are conflicting reports about the number of people injured and the number of shooters. The Pentagon told MSNBC that 12 were shot, and four are dead, and that there's more than one shooter. The MPD however is continuing to tell reporters that only 10 people were shot and that there is only one shooter.
MPD still not going above 10 shot, one shooter.— Martin Austermuhle (@maustermuhle) September 16, 2013
11:10 a.m. The number of D.C. schools on lockdown due to the shooting has risen to 10, reports the Washington Post.
11:06 a.m. The Metropolitan Police Department has set up a location for families affected by the Navy Yard shooting to reunite. Correction from MPD: Navy Yard: family members may reunite at Nationals Stadium Parking Lot B, South Capitol & N St SE
Navy Yard: family members may reunite at Nationals Stadium Parking Lot B, South Capitol & K St SE— DC Police Department (@DCPoliceDept) September 16, 2013
11:05 a.m.: Radio station WTOP and local TV affiliate FOX 5 are both reporting that a second shooter is "down."
2 shooters down by police fire not sure alive or dead says Ed Zeigler, Naval District Washington. Doesn't know if there are other shooters.— Kathy Stewart (@KStewartWTOP) September 16, 2013
11:00 a.m. NBC4 reports that more shots were just fired at the D.C. Navy Yard.
10:54 a.m. Reuters captures an image of a police helicopter pulling up what appears to be a shooting victim. (via @jaredbkeller)
10:45 a.m. Navy spokesperson Ed Buclatin tweets that at least eight people have been injured and four have been killed. He also says that there are "at least" two shooters involved.
10:42 a.m.: The ground stop at Reagan National Airport has been lifted, meaning flights may resume departing, landing, and unloading.
10:38 p.m. D.C. police rushed to block off exits to Washington, D.C.'s Navy Yard this morning after learning that a gunman had opened fire inside the Naval Sea Systems Command Headquarters shortly after 8 a.m.
The Washington Navy Yard is a secure naval facility not far from Nationals Park in Southeast Washington, D.C. It currently serves as a ceremonial and administrative center for the U.S. Navy, home not only to the Naval Sea Systems Command where this morning's shooting reportedly began, but also to the Naval Historical Center and the U.S. Navy Judge Advocate General's Corps.
While initial reports said that only one gunman was responsible for shooting as many as 10 people—eight civilians and two police officers—the Washington Post was reporting as of 10:13 a.m. that this morning's shooting involved three people, and that while one of them has been neutralized, two more may still be unaccounted for.
Six nearby schools have been placed on lockdown, according to WTOP. A D.C. Fire Department Twitter feed reports that EMS workers are "currently triaging about 40 people who just evac'd, ambulatory, no apparent [injuries]."
Top image: Police work the scene on M Street, SE in Washington near the Washington Navy Yard on Monday, Sept. 16, 2013. (AP Photo/Jacquelyn Martin)