New York Gov. Andrew Cuomo said Sunday that part of a nuclear power plant remains offline after a transformer fire that has created another problem: thousands of gallons of oil leaking into the Hudson River.

At an afternoon briefing, Cuomo said emergency crews were out on the water near Buchanan, New York, trying to contain and clean up the transformer fluid that leaked from the Indian Point 3 plant.

"There's no doubt that oil was discharged into the Hudson River," Cuomo said. "Exactly how much, we don't know."

Cuomo revealed Sunday that even after the blaze on the non-nuclear side of the plant was quickly doused, the heat reignited the fire, but it was again extinguished.

Oil in the transformer seeped into a holding tank that did not have the capacity to contain all the fluid, which then entered river waters through a discharge drain.

Joseph Martens, commissioner of the state Department of Environmental Protection, said measures were taken to keep the oil from spreading, including setting up booms over an area about 300 feet in diameter in the water.

The cleanup should take a day or two, Cuomo said.

A spokesman for the Nuclear Regulatory Commission, the U.S. regulator for nuclear power, said several thousand gallons of oil may have overflowed the transformer moat.

The reactor itself was deemed safe and stable throughout, said a spokesman for Entergy Corp., which owns the plant. The adjacent Unit 2 reactor was not affected and remained in operation.

The transformer at the Indian Point 3 plant, which is around 30 miles north of midtown Manhattan and surrounded by about 20 million residents, failed on Saturday evening, causing a fire that forced the automatic shutdown.

The fire on the non-nuclear side of the plant was quickly extinguished and the reactor was deemed safe and stable, said a spokesman for owner Entergy Corp.

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

The transformer at Indian Point 3 takes energy created by the plant and changes the voltage for the grid supplying power to New York 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.

"There is no threat to area residents," said Eliot Brenner, director of public affairs for the U.S. Nuclear Regulatory Commission. "They declared an unusual event. That's the lowest of our four situation designations."

An "unusual event" classification indicates a potential security threat or a possible "degradation of the level of safety" at a plant, according to the NRC website. It also means there have been "no releases of radioactive material requiring offsite response or monitoring."

The Indian Point Energy Center in Buchanan supplies electricity for millions of homes, businesses and public facilities in New York City and Westchester County.

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

Cuomo said there had been too many emergencies recently involving Indian Point. Unit 3 was 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.

The environmental watchdog group Riverkeeper issued a statement Sunday saying the latest Indian Point accident proves that the plant should be closed for good.

Wire services