A man was struck and killed by a Brooklyn subway train early Saturday, police said.

The 37-year-old victim was on the tracks at the Crescent Street station in Cypress Hills at about 3 a.m. when he was hit by an oncoming southbound J train, officials said.

He was pronounced dead at the scene.

It was not immediately clear why the man — whose name was being withheld pending family notification — was on the rail bed, police said.