Two NYPD officers were seriously injured in two separate car crashes overnight Sunday, authorities said.

An off-duty NYPD sergeant was riding his motorcycle around 9:12 p.m. Sunday in Brooklyn when he collided with a Nissan sedan that was turning left at Remsen Avenue and Greenwood Road in Canarsie, police said.

The 47-year-old motorcyclist suffered severe head trauma and was rushed to Brookdale University Hospital Medical Center, where he remains in critical condition.

The 26-year-old driver of the sedan remained at the scene and was taken to Kings County Hospital with non-life-threatening injuries, police said. No arrests were made.

Hours later, around 6 a.m., an on-duty officer was helping a broken-down vehicle in Queens when he was struck by a passing car.

The 36-year-old cop was standing on the road, tending to the stuck car in the westbound lane of the Jackie Robinson Parkway near Metropolitan Avenue, when an out-of-control black Infiniti hit him.

The officer was taken to Jamaica Hospital Medical Center in serious but stable condition.

The driver of the Inifiniti remained at the scene and was not immediately charged.