Tokyo, March 12 (IANS) Radioactive cesium has been detected at Japan's quake-damaged Fukushima No. 1 nuclear power plant, indicating an occurrence of a reactor meltdown, Xinhua reported Saturday.

The detection of the leak came after authorities successfully completed the expansion of a three-km evacuation zone to 10 kilometres for residents in the vicinity of the plant, following the radiation reaching 1,000 times the regular level in the operating room, the Nuclear and Industrial Safety Agency said Saturday.

A massive 8.9-magnitude earthquake followed by 10-metre tall tsunami waves rocked the northeastern Japan Friday, killing about 1,000 people. Bodies of over 400 people have been recovered.

The government also issued an evacuation order for residents in the vicinity of Fukushima No. 2 nuclear plant.

The nuclear safety agency said Saturday that residents were not in immediate danger from radioactive leaks, but the plant's operator is set to release pressure in containers housing nuclear reactors that could result in the leak of radioactive substances.

The order to widen the evacuation zone came from Prime Minister Naoto Kan, who visited the facility Saturday.