A spokesperson for the Philadelphia Police Department confirmed to Reuters by email there were "multiple gunshot victims" but said no further details were immediately available.
Just before 8:40 p.m. police officers said they had apprehended a male suspect wearing a ballistic vest and recovered a rifle and handgun in a nearby alleyway, The Philadelphia Inquirer reported.
Both the Inquirer and Philadelphia television WPVI, an ABC News affiliate, reported two of the people shot were juveniles, but it was not clear whether they were among the dead.
Details of the July Fourth-eve gun violence were sketchy, but the shooting was reported to have erupted in the Kingsessing section of southwest Philadelphia.
The shooting came a day after two people were shot dead and 28 others injured, about half of them children, in a hail of gunfire at an outdoor neighborhood block party in Baltimore, Maryland.