PHILADELPHIA (CBS) -- Philadelphia police are searching for a suspect who escaped from a patrol vehicle after he was arrested on Monday morning, authorities said. 

Police said 32-year-old Nafiysh Knox-Schenck was arrested for an open warrant on a firearm violation on West Collum Street in the city's East Germantown section. 

A firearm was taken from Knox-Schenck after he was arrested, police said. But while he was handcuffed in the back of a patrol car, police said he escaped after someone opened the door. It's unclear who opened the rear door to the patrol car, according to police. 

Police said Knox-Schenck fled eastbound on foot on Collum Street and officers weren't able to catch him. 

Police are urging the public not to approach Knox-Schenck. 

Anyone with information about Knox-Schenck's whereabouts is asked to call 911.