Detectives are investigating a crash Thursday night in Lake Grove that left a pedestrian with life-threatening injuries, Suffolk police said.

Benito Martinez, 44, was in a westbound lane of Route 347 when he was struck by a Chrysler minivan driven by Cynthia Smith, 56, about 7 p.m., just west of Moriches Road, police said.

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Smith, of Stony Brook, immediately stopped and called 911, police said.

Martinez, of Port Jefferson Station, was taken to Stony Brook University Hospital with serious injuries, police said.

Smith and her 79-year-old passenger were not injured, police said, and the vehicle was impounded for a safety check. Sixth Precinct detectives said they are continuing the investigation.