A uniformed security guard was critically wounded in a shooting at a gas station near the Philadelphia Zoo Wednesday night, city police said.

The 42-year-old guard had stopped at the Sunoco station at 3750 W. Girard Ave. about 11:15 p.m. to purchase antifreeze and heard a disturbance inside the A Plus Mini Market at the station, police said.

When he went to check, he was shot in the back of the neck, police said.

The guard originally had been identified as an off-duty school police officer.

He was taken to the Hospital of the University of Pennsylvania, where police said he was in critical but stable condition.

Police were looking for the gunman, who fled east on Girard in a green Chevrolet Venture minivan.