An off-duty firefighter was in critical condition Wednesday night ­after crashing his motorcycle into the back of a car in Queens, authorities said.

Police say the firefighter, whose name was not released, struck the vehicle at about 8:30 p.m. on the Long Island Expressway near 108th Street.

He was rushed to New York Presbyterian-Queens Hospital, where he was admitted with life-threatening injuries, authorities said.

Cops say no summons was ­issued to the car driver, and no criminality is suspected.