Japanese authorities detected high level of radioactivity at a reactor in the troubled Fukushima No. 1 nuclear power plant on Sunday, local media reported.

An aerial view shows Fukushima Daiichi nuclear power plant in Fukushima in this March 17, 2011 file photo. From R-L: Reactors 1 to 4 are seen in this picture taken more than 30km (18 miles) offshore from the site shortly before the start of the water-dropping operation. Plant operator Tokyo Electric Power Co said on March 27, 2011 radiation 10 million times the usual level was detected in water that had accumulated at the No.2 reactor's turbine housing unit and a TEPCO official said that workers at the reactor had left to prevent exposure to radiation. (Xinhua/Reuters File Photo)

The operator Tokyo Electric Power Co said the extremely contaminated water may come from the damaged fuel in the reactor.

Japanese authorities also found radioactive iodine 134 was extremely high in water at the reactor. Workers working at the reactor were temporarily evacuated due to the high radiation.

Radioactive iodine which is 1,850 times the legal limit was found in sea near the troubled plant, according to Kyodo. The level had surpassed the figure detected near the drain outlets of the plant on Saturday.

The government's Nuclear and Industrial Safety Agency has found radioactive iodine 1,250.8 times above legal limit in sea near the plant on Saturday. The readings were taken Friday morning about 330 meters south of the plant, near the drain outlets of the reactors at the utility.

The agency added that the radiation will not have a significant impact on fishery products because fishing is not conducted in the area within 20 km of the plant.

Japanese authorities have been stepping up efforts to fix the nuclear power plant crippled by devastating March 11 earthquake and tsunami.

VietNamNet/Xinhuanet