A motorcyclist from Sayville was seriously injured when he struck the back of a school bus Friday morning in East Islip, a crash that shut down westbound Sunrise Highway for three hours, Suffolk County police said.

Duane Thibodeau, 47, was airlifted to Stony Brook University Hospital, police said. He was in serious condition Friday afternoon, a hospital spokesman said.

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Two adults were on the school bus and were not injured, police said.

Thibodeau was riding a Harley-Davidson when he struck the bus at 9:23 a.m. at Exit 45, near Route 111, police said.

The westbound lanes were closed as Third Precinct detectives investigated. Traffic was diverted at Exit 46, Carleton Avenue, before the lanes reopened about 12:30 p.m., police said.

Detectives ask anyone with information to call 631-854-8352.