Washington  - Nuclear safety officials moved Sunday to quell worries about a leak of radioactivity from Three Mile Island nuclear plant, saying that human safety was never endangered.

The incident happened Saturday, when the Pennsylvania plant - the same one that went to the brink of meltdown in 1979 - had what officials called an "unplanned exposure" and sent home 150 workers, media reports said.

John White, a spokesperson for the Nuclear Regulatory Commission, said that federal experts sent to the plant found "nothing ... that indicates safety was ever in jeopardy."

Diane Screnci, another NRC spokesperson, told CNN that there had been a leak within the reactor building that created minor contamination which was "well below regulatory limits."

She said the incident began when containment radiation alarms sounded. Federal experts have been sent to investigate, she said.

The country's worst civilian nuclear accident to date occurred at Three Mile Island on March 28, 1979, when the cooling system malfunctioned in one of the towers, causing a partial meltdown of Unit 2.

For days, many in the central Pennsylvania region around Harrisburg, near where the plant is located, slept with bags packed and boots on in case of disaster and forced evacuation.

The accident, which released radiation and krypton gas, put a decades-long moratorium in many countries on building new nuclear plants that was reinforced with the ensuing 1986 Chernobyl disaster in Ukraine.

After clean-up, Unit 2 has remained mothballed.

But in recent years, nuclear power has enjoyed a popular resurgence and today provides about 16 per cent of the world's electricity supply. During this decade, 14 new plants are being planned for the United States alone. China has about three dozen nuclear power plants in the works. (dpa)