A Montgomery County police officer at the scene of two car crashes on Interstate 270 was struck by a third car Tuesday evening, prompting authorities to shut down the southbound lanes of the highway.

The off-duty officer was taken to a hospital for evaluation of injuries that did not appear to be life-threatening, the county police said.

The incidents occurred about 5:15 p.m.at the point where the eastbound lanes of Route 118 join the southbound lanes of the Interstate.

Two cars had slid off the ramp, as the possible result of slippery conditions, and the off-duty officer had left his marked police car to help their occupants, county police said.

A third car also slid on the ramp and struck the officer and his cruiser, the county police said.

State police said one or more of the crashes occurred on the Interstate, shutting down the southbound lines while an investigation was under way. The lanes were reopened by about 8 p.m.

This report has been updated.