The shooting occurred around 5 p.m. at 15th Street and Girard Avenue in North Philadelphia.
"It appeared that the two shooting victims were standing in a group of about three to five people, and it appeared the shooters were intentionally firing into that crowd," said Philadelphia Police Chief Inspector Scott Small.
Police say three suspects fled the scene on foot.
A 16-year-old boy was shot in both legs and is listed in stable condition. A 17-year-old boy remains in critical condition after being shot in the arms, legs and torso, according to officials.
Small said more than 50 shots were fired near one of North Philadelphia's busiest intersections.
"Oftentimes, the guns have switches that transform them from semi-automatic weapons to fully automatic weapons. That's a very good possibility in this case, since so many shots were fired in such a short period of time," he said.
Police have not released descriptions of the suspects.
Anyone with information is asked to call police at 215-686-TIPS.
(Editor's note: An earlier verision of this story reported three people were shot in the incident.)