Updated

A Washington, D.C. police officer is "fighting for her life" after being wounded early Sunday in a shootout that killed a teenager and sent many people to the hospital, Police Chief Peter Newsham said at a press conference.

Police responded to reports of shots fired shortly before 1 a.m. at a large gathering in the 3300 block of Dubois Place,  part of a residential neighborhood in southeast Washington.

Newsham said 20 people were wounded at the scene. At least 11 of the victims are female.

Christopher "Poppy" Brown, 17, was shot and pronounced dead at a nearby hospital, Fox 5 DC reported. An off-duty DC Metro police officer was shot and is "struggling for her life right now," Newsham told reporters at the scene, standing alongside Mayor Muriel Bowser.

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The rest of the victims had non-life-threatening injuries. Some walked to a nearby fire station and hospital after being grazed by bullets.

The gunfire erupted at a cookout with hundreds of people gathered outside, a neighbor told WUSA. Several social media posts advertised the annual “34th-n-EAT” block party to be held in the area Saturday night with bottles of alcohol and a DJ.

Newsham said a dispute broke out at the gathering and several people produced weapons and exchanged gunfire.

Police investigate a shooting that broke out in southeast Washington, D.C. early Sunday morning. (WTTG)

“It was terrible. You had quite a few people laying on the ground, people ducking under cars,” one neighbor told WTOP.

More than 20 responding units, including D.C. Fire and EMS, arrived at the scene. The street was littered with bullet casings, as well as car keys and other belongings left behind by people fleeing the gunfire.

No arrests have been made. Police remained at the scene and continued to investigate Sunday morning.

“Sadly, several people who have no regard for human life open fire at what had been ... people together enjoying themselves,” Bowser said.

The mayor said the gathering was illegal on a number of levels.

“It is illegal to drink on the street in the District of Columbia; it is illegal to smoke marijuana on the street in the District of Columbia. It is illegal to be in a gathering of more than 50 – all of those things are not good," she said. "And, sadly, when you put illegal guns in the hands of people willing to use them, it means some person could lose her life or some people could lose their lives."

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“As a community, it’s really important that we have zero tolerance for this type of activity; that we support the Metropolitan Police Department … and that may mean that people will have to go to jail.”

This is a breaking news story. Check back for updates.