One person was killed Monday night in Flanders and three others were injured in a crash that involved at least four vehicles, Southampton Town police said.

The 8 p.m. crash on Flanders Road, near Fanning Road, left investigators a complicated scene that stretched at least a quarter-mile with four to five vehicles and also caused a separate collision with more vehicles, likely from rubbernecking, Sgt. Joseph D’Arce said.

It was not immediately clear what happened, he said, but the preliminary investigation leads police to believe it started when one motorist “slightly” veered into an oncoming lane of traffic and sideswiped another vehicle.

Details on the person who died were not immediately available.

One person sustained serious injuries and was flown to Stony Brook University Hospital, while the two others injured were taken to nearby hospitals, police said.

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Details on the second crash was not immediately available.

Flanders Road, a main thoroughfare for the area, was shut down in both directions between Long Neck Boulevard and Pleasure Drive, police said.

D’Arce said detectives and many patrol units remained at the scene late Monday night.