According to the Nuclear and Industrial Safety Agency, radioactive iodine-131 at a concentration 1,250.8 times the legal limit was detected Friday morning in a seawater sample taken around 330 m (1,083ft) south of the plant, near the drain outlets of its troubled four reactors.

"The increased level of radiation in the seawater will have no influence on marine life," Edano said during a briefing over the situation at the Japanese nuclear accident.

Kyodo news agency quoted government officials earlier as saying that the radiation levels in seawater do not pose an immediate risk to human health but that they are well above normal levels and thus fan concerns over fish products in northeastern Japan.

The confirmed death toll from the March 11 earthquake and tsunami stands at more than 10,000, according to police, and over 17,440 are listed as missing.

Operations have continued to restart the cooling systems at Fukushima's six reactors to try to avoid a major radioactive release.

The Japanese government on Friday asked people still living within 30 km (19 miles) of the damaged plant to leave due to shortages of food and other essentials.