A meltdown may have occurred at at least one nuclear power reactor in Japan, the country’s chief cabinet secretary, Yukio Edano, said Sunday.

He also said that authorities are concerned over the possibility of another meltdown at a second reactor.

“We do believe that there is a possibility that meltdown has occurred. It is inside the reactor. We can’t see. However, we are assuming that a meltdown has occurred,” he said of the No. 1 reactor at the Fukushima Daiichi nuclear facility. “And with reactor No. 3, we are also assuming that the possibility of a meltdown as we carry out measures.”

Edano’s comments confirm an earlier report from an official with Japan’s Nuclear and Industrial Safety Agency, who said, “we see the possibility of a meltdown.”

A meltdown is a catastrophic failure of the reactor core, with a potential for widespread radiation release. However, Toshihiro Bannai, director of the agency’s international affairs office, expressed confidence that efforts to control the crisis would be successful.

The efforts to control the temperature of atomic material, by pumping in sea water and boron, are taking place at the same facility where four were hurt late Saturday in an explosion. Edano said only a “minor level” of radiation has been released into the environment — saying it all came from a controlled release of radioactive steam, insisting there have been no leaks.

“We do not believe it is harmful to human health,” he said.

About 180,000 people are being evacuated from within 10 to 20 kilometers (6 to 12 miles) of the Daiichi plant — which is in addition to the thousands that have already been taken away who live closer by. More than 30,000 more people were being evacuated from their homes within 10 kilometers of the Fukushima Daiini nuclear facility located in the same prefecture.

(Source: CNN)