The shooting occurred just after 12 a.m. Monday near 39th and Melon streets as a block party was breaking up about a block away.
Cynthia Young said what had been a quiet night in this part of Mantua ended in a hail of gunfire.
"'Pop, pop, pop!'" she said, reliving the moment the shots rang out. "(I was) scared to get up."
Investigators say they recovered a total of 31 spent shell casings at the scene.
Initial reports indicated five people had been hit.
Authorities now say four people - all in their late teens and early 20s - suffered gunshot wounds.
One, an 18-year-old man, was critically wounded.
There has been no word on a possible motive.
The gunman reportedly fled in a vehicle, and remains on the loose.
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