It was not clear whether the gunman knew anyone in the car or what sparked the shooting late Saturday, Camden County prosecutor's spokesman Jason Laughlin said. The gunman eventually fled and remained at large Sunday, authorities said.
The car was parked in an alley when the masked man approached and got in on the driver's side, Laughlin said. He fired several shots, killing the 18-year-old driver, Jewel Manire, and Khalil Gibson, 20, of Camden.
The spray of bullets wounded a 20-year-old woman in the face, a 16-year-old in the head and another 16-year-old in the arm, Laughlin said.
After the gunman stopped shooting, he pushed aside Manire's body and drove off with all the victims inside except the teenager who was shot in the arm. She had managed to escape and called 911.
The car was driven to a nearby dirt road, where the 20-year-old woman also jumped out and ran off. The gunman briefly pursued her but could not catch her, and he soon ran away.
He was described as Hispanic and about 6 feet tall. He wore a black mask over the lower part of his face and yellow latex gloves.
All three wounded victims remained in the hospital Sunday, two in critical condition.
Camden, a city of about 80,000 that sits along the Delaware River across from Philadelphia, continually ranks as one of the most dangerous and poorest in the U.S. The two fatalities bring the city's homicide total this year to 50, eight short of the record reached in 1995.
City officials are trying to replace the police department with a force run by the county, a move that would circumvent union rules in order to increase the number of officers while keeping costs the same.
Last month, authorities said they were trying to determine whether a contaminated batch of PCP was going around town after a child was decapitated and two other children's throats were slashed by people believed to be on the illegal drug. A man charged in the attack admitted to police that he had smoked "wet," a combination of PCP and marijuana.