A boat exploded off the coast of City Island in the Bronx Saturday afternoon, bursting into flames that injured three passengers and caused a thick black plume of smoke, officials said.

The 30-foot vessel ignited in the Long Island Sound around 1:40 p.m., an FDNY spokesperson said.

Three people were taken to area hospitals with minor injuries, the spokesperson said.

The cause of the explosion wasn’t immediately clear, cops said.

Dramatic video captured flames ripping through the craft and a thick plume of black smoke extending into the sky above.

Twenty-one units with 79 firefighters responded to the incident, the FDNY said.