A man was struck and killed by a train at an Upper East Side station just before 8 a.m. Wednesday, the MTA said.

The man, who has not been identified, was hit by a downtown No. 6 train at the 77th Street station on Lexington Avenue. He was pronounced dead at the scene, officials said. 

Police said a witness saw the man jump in front of the train, but the investigation is ongoing.

Due to the incident, No. 6 trains were running express between 125th Street and Grand Central-42nd Street in both directions. Downtown No. 5 trains were also rerouted along the No. 2 line. 

The MTA said regular service resumed with delays around 9:35 a.m.