A New York City subway worker is dead after he was dragged by a train, according to the Metropolitan Transportation Authority.

The incident occurred early Wednesday morning just south of the Macy’s-Herald Square station in Manhattan, MTA officials say. The employee, a 57-year-old man, was working as a flagger when he somehow got caught on a moving D train and was dragged underneath it, per the MTA. He was rushed to a nearby hospital, where he was pronounced dead.

As of late Wednesday afternoon, MTA officials still hadn’t figured out exactly what had happened. “There was work taking place, scheduled work,” says MTA Chair Janno Lieber. “The fellow was flagging, and it’s very much still under investigation on what went wrong.” The National Transportation Board is investigating, Lieber adds.