An on-duty Long Island motorcycle cop was critically injured Saturday by a hit-and-run driver who was later arrested, authorities said.

The unidentified Nassau County Police officer was on routine patrol in North Bellmore when he was struck by a Subaru driven by Hussam Rajab at the intersection of Bellmore and Alice avenues, police said.

Rajab fled the scene, but was caught 30 minutes later over 3-miles away on Sunrise Highway, cops said. He was charged with leaving the scene of an accident with a serious physical injury.

The officer was taken to Nassau University Medical Center in critical, but stable condition, authorities said.