An explosion on a boat carrying raw sewage that was docked on the Hudson River in New York City killed a longtime city employee, authorities said.

Another worker on the city-owned Hunts Point vessel was injured and taken to the hospital after the blast about 10.30am Saturday near the North River wastewater treatment plant, according to city deputy assistant chief David Simms of the fire department. A third worker refused medical treatment.

The cause of the explosion was under investigation, but the New York City mayor, Eric Adams, said criminal intent was not suspected. The men on the boat, which takes raw sewage from the city to be treated, were doing work involving a flame or sparks when the explosion occurred, said the US coast guard.

First responders found a 59-year-old man unconscious in the river, New York police said, and he was declared dead at the scene.

The man had been a longtime employee of the city’s environmental protection department. The mayor said he was “a devoted public servant who gave 33 years of service to the New York City, and our hearts go out to his family, friends, and colleagues during this painful time”.

The blast spread raw sewage over the deck of the boat, and firefighters and other first responders had to be decontaminated, Simms said.