The shootout happened at a Chinese takeout restaurant at 27th and Dickinson streets at 10:30 p.m. on Monday.
More than 40 rounds were fired during the gun battle, according to police.
A 45-year-old man was transported by police from the scene with gunshot wounds to the leg.
The three other victims, a 23-year-old man and two 21-year-old men, showed up at Penn Presbyterian Hospital on their own.
Another 21-year-old man was also taken to Cooper Medical Center in Camden, New Jersey.
Police believe one of the wounded patients was also a shooter and is being held as a suspect.
A semiautomatic gun with an extended magazine was recovered at the scene and surveillance cameras recorded the shooting, police said.
The shootout hit people inside and outside the takeout restaurant. Police found at least a dozen shell casings where customers were waiting for orders.
A child was inside at the time but, fortunately, was not injured.
The vehicle used to take three of the victims to the hospital is being held by police.
Detectives are looking for more information from witnesses.
Police say a dark-colored SUV, possibly a Jeep, was seen fleeing south on 27th Street.
Anyone with information is asked to contact the Shooting Investigation Group at 215-686-8270.
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