A dirt bike rider is fighting for his life after being struck by a hit-and-run driver in the Bronx yesterday, authorities said.

The 22-year-old man was traveling northbound on Clay Avenue at 174th street on a Kawasaki dirt bike at 7 p.m. when he was rear-ended by a red four door sedan, police said.

The car then fled the scene.

The victim was transported to Saint Barnabus Hospital in critical condition, suffering from head trauma, police said.

Authorities said he was unconscious and bleeding heavily from the head when the ambulance arrived.

No arrests have been made.