Two gunmen ambushed a backyard party near Pittsburgh on Wednesday, killing at least five people and injuring several, media and police said.
Four women and one man were shot and killed, and three more were wounded in the attack at a residential neighborhood in Wilkinsburg, about 8 miles (13 km) east of the city, news station WPXI said.
"I heard at least 20 shots," a witness, Kayla Alexandra, told WPXI.
The shooters fled after the ambush and were still at large, the news station added.
The attack in Wilkinsburg, a borough of about 16,000 people, is the latest in a series of mass shootings that have elevated gun control as an issue in the U.S. presidential elections.
Four people were declared dead at the scene of Wednesday's attack, said Lieutenant Andrew Schurman of the Allegheny County Police Department.
Four more victims were taken to nearby hospitals, but one died from her wounds. The other three were in critical or stable condition, Schurman said.
Dozens of shell casings littered the pavement of an alleyway near the site, where police were gathering evidence and talking to witnesses, media reports said.
Wilkinsburg has many lower- and middle-income residents, demographic data shows.