Three people were killed and another injured in a shooting in a Philadelphia residential neighborhood Friday, authorities said.

It wasn't immediately known what spurred the shooting, which was reported around 3:35 p.m., or how many shooters may have been involved.

PHILADELPHIA BUSINESS OWNER, ACCOMPLICE CHARGED FOR STARTING BLAZE THAT KILLED FIREFIGHTER

Responding officers found one victim on the front porch of a house and another just inside the home, while the third victim was on the sidewalk, authorities said. All three were pronounced dead at the scene, and their names have not been released.

The wounded victim was taken to a hospital by an unknown person, authorities said, and was listed in critical condition. Their name and further details on their injuries were not disclosed.

PHILADELPHIA 5-YEAR-OLD SHOOTS HIMSELF WHILE PLAYING WITH MOTHER'S GUN: POLICE

Police found a gun at the scene but did not say if it was used in the shooting.

Authorities said they were looking for those responsible for the shooting, but did not provide further details. No arrests have been made.