A transformer failed Saturday at the Indian Point nuclear power plant in suburban New York, causing a fire that forced an automatic shutdown of a reactor. The fire was quickly extinguished and the reactor was deemed safe and stable, said a spokesman for owner Entergy Corp.

The transformer at Indian Point 3 takes energy created by the plant and changes the voltage for the grid supplying power to the state. The blaze, which sent black smoke billowing into the sky, was extinguished by a sprinkler system and on-site personnel, Entergy spokesman Jerry Nappi said. Westchester County police and fire were on site as a precaution.

It was not immediately clear what caused the failure, or whether the transformer would be repaired or replaced. Nappi said there were no health or safety risks. It's unclear how long the 1,000-megawatt reactor will be down. Entergy is investigating the failure.

The plant's adjacent Unit 2 reactor was not affected.

The Indian Point Energy Center in Buchanan, 35 miles up the Hudson River from midtown Manhattan, supplies electricity for millions of homes, businesses and public facilities in New York City and Westchester County.

In accordance with federal regulations, the U.S. Nuclear Regulatory Commission, state, county and local officials were notified of the event, considered the lowest of four emergency classifications for U.S. nuclear plants.

Gov. Andrew Cuomo was briefed on the failure at the site and said officials would review how the emergency was handled to determine if anything could have been done better. Cuomo said the fire had caused oil to leak and could possibly spill into the Hudson River, but crews were working containing it.

"These situations we take very seriously. Luckily this was not a major situation. But the emergency protocols are very important," he said. "I take nothing lightly when it comes to this plant specifically."

But he said there had been too many emergencies of late. Unit 3 had been shut down Thursday morning for an unrelated issue, a water leak on the non-nuclear side of the plant. It was repaired and there was no radioactive release, Nappi said. In March, Unit 3 was shut down for a planned refueling that took about a month.

A spokeswoman for the NRC said an agency inspector assigned to the plant was headed there, and the agency would follow up as Indian Point troubleshoots.

Spokeswoman Diane Screnci said there was no impact on the public. She said it was not out of the ordinary for a transformer to have a problem, and noted that it was on the non-nuclear side of the plant.