According to the police report, the gunfire was heard just before 8:30 p.m. local time (0030 GMT on Tuesday) and received multiple reports of a male armed with a rifle shooting in the Kingsessing section of Southwest Philadelphia.
Official reports state that at least two juveniles were among those shot, but their conditions were not immediately known. They have been transported to nearby hospitals.
The police said that about 10 minutes after the shots rang out, police officers reported they had apprehended the suspect, who was wearing a bulletproof vest, and that they had recovered a rifle and a handgun in a nearby alleyway.
"Horrified by the reports of a shooting in Southwest Philadelphia," tweeted Philadelphia Mayor Jim Kenney, adding, "My heart is with the loved ones and families of everyone involved, and I send my prayers to the victims."
The mayor also expressed his thanks to police officers "for their brave response and successful apprehension of a suspect." This violence must stop, he noted.
According to the Gun Violence Archive (a nonprofit group which defines a mass shooting as one in which at least four people are shot, excluding the shooter), at least 341 mass shootings have happened across the United States so far this year.