Police said they had not made any arrests in the shooting, which occurred at a house party in the West Philadelphia neighborhood.
Before daybreak, two more people had been killed, WCAU-TV reported. One was found dead at about 2:30 a.m. in the Frankford neighborhood, while the third died at a hospital a few hours after police responding to a call of trouble at a North Philadelphia home found three people wounded.
In recent years, the City of Brotherly Love has had the highest homicide rate among the 10 largest U.S. cities. In 2011, the rate was more than 20.7 per 100,000 residents, while the runner-up, Chicago, had 15.7 per 100,000.
In 2012, 329 homicides were reported in the city, up from 324 in 2011.