A transformer exploded at the Indian Point Nuclear Power Facility in Westchester, New York, on Saturday, police said.
There were no reports of injuries in the blast and resulting fire, which Indian Point Energy said was caused by a "transformer failure" that happened around 6 p.m.
"Saw a huge ball of black smoke and then alarms audible across the river," Gustavus Gricius, who witnessed the explosion, said.
The fire started up again after being extinguished but has since been put out, officials said. There are no ongoing emergency threats.
Governor Cuomo said a review of the plant will be done to make sure all safety protocols were followed correctly. The governor has been vocal about his concern over having a nuclear power plant in the area and said no situation at a nuclear plant is minor.
There is now concern that the foam used to extinguish the fire could seep into the nearby Hudson River, Cuomo said. He said crews are working to keep foam out of the storm drains.
Indian Point Energy said there was no danger to employees or the public and that Unit 3 of the facility safely shut down as designed after the transformer failed.
Unit 3, which supplies 5 percent of the power to New York state, sits near the Hudson River, about 300 to 400 feet away from the reactor building, which is reinforced by a 4 to 6 foot wall of steel and concrete.
A spokesperson for Entergy, which owns the plant, said that a sprinkler put out the initial fire with the help of an on-site fire brigade.
Entergy said the fire was an "Unusual Event" -- the lowest of four emergency response classifications.
Dave Lochbaum, who is the director of the Nuclear Safety Project, said the transformer is in the switch yard outside the plant, but within the security perimeter.
He said oil is used to cool the transformers and that an electrical short may have caused the explosion.
"Transformer explosions are not uncommon -- they happen roughly three or four times a year across the industry," Lochbaum said.
He said it's unlikely that such an explosion would cause any harm to the public.
Engineers and inspectors are investigating what caused the transformer to fail.
This is a developing story. Check back here for updates.