A man was fatally struck by a train at an Upper East Side subway station Tuesday morning, authorities said.

The 53-year-old man was lying on the tracks at the 77th Street station when a northbound No. 6 train rolled over him around 4:30 a.m.

The man was pronounced dead a short time later.

It was not immediately clear how the man ended up on the tracks and police were still investigating the incident Tuesday morning to determine if any criminality was involved, officials said.