A worker cutting up a fuel tank with a gas-powered demolition saw was critically burned in a Mastic Beach explosion Tuesday when the fumes or fuel remnants ignited, Suffolk police said.

Patrick Rooney, 21, was taken to Stony Brook University Hospital, where he underwent surgery at night and was in critical condition, police said.

The explosion happened at the East End Environmental Services, located at 123 Whittier Drive, where Rooney was in the rear yard disposing of an old, oil tank that was larger than ones used for homes, police said.

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Several 911 calls about 1:15 p.m. alerted officers to the fire and explosion, police said.

Seventh Precinct detectives are investigating. Officials notified the Occupational Safety and Health Administration, part of the U.S. Labor Department.