UPPER MERION, Pa. (CBS) — Authorities say a police officer was struck during a multi-vehicle accident in Montgomery County on Thursday evening.

The accident happened on Route 202 and South Henderson Road in Upper Merion around 5:45 p.m.

Police say an Upper Merion Township police vehicle was stopped for a red light at the intersection when they were struck from behind.

The impact of the collision pushed the police vehicle into the rear of another stopped vehicle and over the center median. Police say the officer’s vehicle crossed both lanes of Route 202 southbound before coming to rest. A total of five vehicles were involved in the chain-reaction collision.

Two drivers and the police officer were transported to area hospitals.

The officer was treated and released.

The condition of the others injured is unknown at this time.

Police believe the driver who struck the police vehicle suffered an unknown medical emergency.

The crash remains under investigation.