Four women and one man were shot and killed in a residential neighborhood in Wilkinsburg, about 8 miles (13 km) east of the city, news station WPXI said, adding that the suspects were at large.
“I heard at least 20 shots,” a witness, Kayla Alexandra, told WPXI, which reported that at least two gunmen were involved in the shooting.
Other regional media said seven or eight people were shot.
Police were not immediately available for comment.
Several reporters in the area Tweeted photographs of ambulances and police cars. Dozens of shell casings littered the pavement of an alleyway at the scene, media reports said.
Wilkinsburg is a borough of about 16,000 people, with many lower- and middle-income residents, demographic data showed.