A lone shooter who wounded four people in an upscale Washington neighborhood killed himself before being apprehended, the city's police chief said Friday evening.

The Connecticut Avenue-Van Ness neighborhood of the US capital -- where multiple schools and embassies are located -- was swarmed by law enforcement and locked down after gunfire erupted in the area Friday afternoon.

Assistant police chief Stuart Emerman said three people had been taken to the hospital -- two adults who were in critical but stable condition and a 12-year-old girl with a minor gunshot wound.

Another individual with a graze wound to the back was treated at the scene, Emerman added.

"The suspect that we believe is responsible for this is now deceased," Washington Police Chief Robert Contee said at a news conference Friday night.

He said the suspected shooter took his own life as police officers breached the fifth-floor apartment where he was located and that they found a "sniper-type set up with a tripod."

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While no motive was yet known, "obviously his intent was to kill and hurt members of our community," Contee added.

A video shared widely on social media showed lengthy bursts of automatic gunfire toward multiple people who ran for cover, apparently taken from the perspective of the shooter.

"It looks very much to be authentic," Contee said of the video, but clarified that it still needed to be forensically confirmed and it was not known if the video was live-streamed or uploaded afterward.

More than six guns were recovered from the fifth-floor apartment, Contee said, as well as "multiple, multiple rounds of ammunition."

Photographs posted later by the police department on Twitter showed three assault-style rifles with scopes laying on a table with a tripod in the background as well as a single handgun.

Contee said that police believe the weapons were obtained legally based on preliminary information.

The shooting comes a little over a week after a gunman opened fire on a New York City subway, injuring 23.

That suspect was apprehended after a day-long manhunt and has been arraigned on terror-related charges.