Two police officers and four civilians were wounded on Friday during a shooting spree in Philadelphia where the suspect was later killed by responding officers, police said.

Sergeant Sylvia Young, a 19-year veteran of the department, was shot at least eight times by an approaching gunman as she sat in her vehicle late at night, Philadelphia Police Commissioner Richard Ross said.

"He just walks up on her ... he just fired. He didn't say anything," Ross told a news conference, noting that the suspect fired about 15 rounds into Young's vehicle.

Nearby officers heard the gunshots and began pursuing the suspect on foot. During the chase, the suspect fired shots into a tavern, striking a security guard in the leg, Ross said.

He then used a woman from the bar as a shield before shooting her. He later fired into a car, seriously wounding a man and woman, he said.

The chase ended when the gunman exchanged gunfire with police in an alley, wounding a University of Pennsylvania police officer. The shooter was killed during the gun fight, Ross said.

"We have a lot of unanswered questions...this is a completely bizarre situation," he said.

The officer shot in the alley was expected to survive and the conditions of the wounded civilians was not immediately clear.

"Some civilians are not in good shape at all," Ross said.