BUCHANAN, N.Y. –– A leak in a steam generator at a Hudson River nuclear power plant resulted in a brief release of radioactive steam but it was below dangerous levels, power company officials said.

Con Edison, which owns and operates the Indian Point 2 plant in northern Westchester County, declared an alert, the second of four increasingly serious emergency classifications, company spokesman Michael Spall said.

There were no immediate reports of evacuations.

The size and duration of the leak had not been measured.

Spall said the plant was shut down, but there had been "a momentary release of radioactive material to the environment, below any level that poses a threat to the safety of plant personnel or the public."

Radioactive steam was released for "a few seconds" and initially was held within the plant's containment building, the sealed concrete building that holds the reactor, Spall said. Later it was determined that some steam also was released into the air surrounding the plant, Spall said.

He described the plant as stable but said the alert would last several hours overnight as the shutoff reactor is cooled.

Although county officials activated the emergency operations center in White Plains, they were "confident the situation is under control," county spokeswoman Adele Dowling said.

The accident occurred at 7:29 p.m. in a tube used to carry hot, radioactive, high-pressure water to a pool of cool, non-radioactive water, Spall said. When the hot water hits the cool water, steam is produced, which turns a turbine and generates electricity.

Federal, state and local authorities were notified, Spall said.

The alert was the first in the plant's 16-year history, Spall said.