The exterior of reactor No. 3 at Fukushima Daiichi nuclear plant is seen in this still image taken from undated file video footage. Japan battled to contain a radiation leak at an earthquake-crippled nuclear plant on March 13, 2011, but faced a fresh threat with the failure of the cooling system in a second reactor. [Photo/Agencies]

TOKYO - Japanese Prime Minister Naoto Kan said Sunday the nation is now facing the worst postwar crisis following Friday's 9-magnitude earthquake that triggered massive tsunami and caused problems at a nuclear power plant in Kukushima Prefecture.  

The prime minister told a televised press conference that the situation surrounding the nuclear power plant continues to be in an alarming state. He called for united efforts to rebuild the nation.

So far a total of 12,000 people have been rescued after the quake, Kan said, as police said the confirmed death toll from quake tops 1,000.

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The death toll from the devastating earthquake and tsunami that hit northeastern and eastern Japan will likely surpass 10,000, the Miyagi police chief said Sunday while  millions of survivors remained without drinking water, electricity and proper food along the pulverized.

As rescue efforts are being mobilized nationwide, the nation is facing a crisis at one of two affected nuclear plants.

Japanese authorities scrambled to control overheating reactors at the quake-hit Fukushima No.1 nuclear power plant, and some 180,000 people joined more than 450,000 other evacuees from quake- and tsunami-affected regions by moving out of a 20-kilometer radius from the plant a day after one of its reactors partially melted Saturday, Kyodo News said.

The government rated the incident at Fukushima No.1 nuclear power plant at level four on an international scale of zero to seven on Sunday, in a sign that radiation risks are mounting in Japan.

Two radioactive substances, cesium and radioactive iodine, have been detected near the No.1 reactor of the plant, where radiation rose to as high as 1,204 micro sievert, compared with the legal limit of 500, according to Tokyo Electric Power Co.(TEPOC), operator and owner of the Fukushima plants.

The No. 3 reactor at the plant lost its ability to cool the reactor core earlier Sunday, becoming the sixth reactor that lost the function. And a hydrogen explosion is possible at the No.3 reactor, Japanese Chief Cabinet Secretary Yukio Edano said Sunday.

Sea water has been injected into the reactor to prevent it from overheating, said Edano. "This will result in some radiation leakage, although at a level that won't affect peoples' health. It will help stabilize the situation," he said, acknowledging the core of the reactor may have been deformed due to overheating.

Pressure has been successfully released at the reactor following the injection of water, according to the latest Sankei Shimbun report.

Earlier, Edano said at an emergency press conference that the radiation briefly jumped to 1,204 micro sievert at the plant. The number of people exposed to radiation has risen to 22. Authorities prepared to distribute iodine to protect people from radioactive exposure.

Rescue workers were scanning people arriving at evacuation centers for radioactive exposure. In the neighboring Ibaraki Prefecture, radioactive monitor was set up.

Two experts from the US Nuclear Regulatory Commission were headed for Japan to check on the problem.

The top government spokesman warned that there are still 114 people staying within a 10-km radius of the Fukushima No.1 nuclear power plant and 180,000 in the 20-km evacuation zone.