1 dead and 3 others, including cop, injured in DC shooting: Police

A 15-year-old boy has died and three adults, including a police officer, were injured in a shooting in Washington, D.C., Sunday night, officials said.

The shooting took place near 14th and U streets Northwest, in a popular area filled with stores, restaurants and bars. The area played host to "Moechella," a free concert celebrating Juneteenth.

The Metropolitan Police Department had reported an earlier, separate incident at the concert, when a fight was broken up, MPD Chief Robert Contee said.

Shortly after that, there was a secondary incident, Contee said, during which "people started to scatter" and some were "being trampled." The MPD shut down the concert because it appeared it was "unsafe," police said.

The incidents happened between 6:30 and 8:30 p.m., police said, at an unpermitted event associated with Moechella. Police said "hundreds of people" had gathered on the block, and the MPD assisted in containing the crowd to the sidewalk.

While rendering aid to people caught in the stampede, a firearm was recovered, Contee said.

According to the MPD, several people were shot in the wake of the previous incidents.

Police said the firearm used in the shooting has not been recovered, and there is no suspect in custody at this time.

The two adult victims and the police officer are recovering at an area hospital, police said.

The D.C. Police Union tweeted that one of its members had been shot, was transported to the hospital "and is in stable condition."

The Bureau of Alcohol, Tobacco, Firearms and Explosives Washington Field Division said it was assisting the MPD.

ABC News' Ben Siu contributed to this report.