Detectives yesterday were probing the death of a 45-year-old New Jersey man who plunged four stories to his death outside the Port Authority Bus Terminal.

Sean Anderson, of Bayonne, was spotted by at least two witnesses leaning against a railing of the terminal’s ramp at about 8 p.m. Sunday, sources said.

He reportedly leaned backward suddenly and plummeted 40 feet onto West 41st Street near Ninth Avenue, the sources said.

Police were probing whether alcohol played a role in the death, which appeared to be accidental.