NYPD officers stand guard near the Penn Station following an early morning shooting in Manhattan, Nov. 9

NEW YORK — A 43-year-old man was killed and two men, aged 45 and 48, were wounded in a shooting early Monday at an entrance to New York City’s Penn Station transportation hub in Manhattan, police said.

Police said they were searching for the shooting suspect, a heavy-set man wearing a hooded sweatshirt, and two other men who were possibly connected to the incident.

An altercation began at about 6 a.m. ET in a McDonald’s restaurant near Penn Station, where the gunshot victims were drinking coffee together, New York Police Department Chief of Detectives Robert Boyce told reporters.

The shooting suspect entered the restaurant and briefly spoke with the group before leaving, Boyce said.

When the victims left the restaurant and entered a stairwell leading to a nearby subway station, the suspect followed them and opened fire, police said.

Investigators did not know what prompted the gunfire at the intersection of West 35th Street and 8th Avenue, New York police officer Christopher Pisano said.

The victims did not appear to know the assailant, police said.

Several people near the shooting scene told reporters they knew the victims from a local methadone treatment center.

“We don’t believe this had anything to do with the methadone clinic,” Boyce told reporters. Still, he said police were working to determine whether the men were patients at the clinic.

The two men who were wounded were in serious condition and taken to Bellevue Hospital, the New York Police Department said in a statement. It did not identify the victims, saying the men’s families had not yet been notified.

Streets in the area were closed due to the investigation.

Penn Station is a major railway hub, serving both the Amtrak national passenger rail service and commuter lines linking New York to New Jersey and its eastern suburbs.