Japanese authorities have successfully released pressure from the quake-stricken Fukushima No. 1 nuclear reactor and thus avert a potentially catastrophic meltdown, the Nuclear and Industrial Safety Agency said Saturday.

Release of radioactive gas won't be at a level dangerous to health, said a spokesperson for the agency.

Tokyo Electric Power Co. (TEPCO), which operates the Fukushima nuclear power plants, said that venting gas from a containment vessel of the No. 1 reactor had been successful in reducing perilously high pressure levels.

TEPCO will also repeat the procedure at its adjacent No. 2 plant, also faltering after the reactors were damaged by Friday's massive earthquake and tsunami.

Prime Minister Naoto Kan said he couldn't rule out the possibility of a radiation leak from the No. 2 plant.

Earlier in the day workers frantically struggled to cool the facility and restart its quake-damaged diesel generators to avoid a total meltdown, agency officials said.

The massive earthquake and tsunami that struck northeastern Japan cut the supply of off-site power to the plant on Friday and diesel generators intended to provide back-up electricity to the cooling system subsequently failed.

Japan's Ground Self Defense Forces arrived Saturday to ensure the safe evacuation of local people living near the two stricken nuclear plants.