Nuclear plant operator TEPCO is working on ending the Japan nuclear crisis as radiation levels in the sea have spiked.
Engineers are battling to empty radioactive water from one of the six damaged reactors at the Fukushima Daiichi plant so they can start repairing its cooling system and regain control of the reactors.
The nuclear crisis has been rated on a par with Chernobyl, the world's worst nuclear accident, but TEPCO said the situation at the plant had stabilised.
"We are working out the specific details of how to handle the situation so they can be disclosed as soon as possible," TEPCO president Masataka Shimizu said.
"We are making the utmost effort to bring the reactors at Fukushima Daiichi to a cold shutdown and halt the spread of radiation."
A series of strong aftershocks this week has also slowed the recovery effort at the Fukushima Daiichi plant due to temporary evacuations of workers and power outages.
Radiation readings in seawater near the plant spiked last week, according to Japan's Nuclear and Industrial Safety Agency (NISA).
Seawater samples showed that radiation in the sea off Minamisoma city near Fukushima Daiichi rose to 23 times the legal limit, said Hidehiko Nishiyama, a NISA deputy director-general.
"At one point we had detected high levels of radiation on the coast so I think it is drifting somewhat as one chunk of water," he said.
"While we think it's not harmful to human health, we will continue to monitor closely."
Nishiyama said the decision to raise the severity of the incident from level 5 to 7 - the same as the Chernobyl disaster - was based on cumulative quantities of radiation released.
Experts have pointed out the two crises are vastly different in terms of radiation contamination.
The total cost of the triple catastrophe has been estimated at $300 billion, making it the world's most costly natural disaster, and TEPCO could be liable for compensation claims as high as $130 billion.
Small amounts of strontium, one of the most harmful radioactive elements, have also been found in soil near Fukushima Daiichi.
Japan expanded the 20 km evacuation zone around the plant because of high levels of accumulated radiation.
No radiation-linked deaths have been reported and only 21 plant workers have been affected by minor radiation sickness.
Diplomatic tension could be sparked with Japan's neighbours over radioactive fallout, with Chinese Premier Wen Jiabao saying he was "concerned" about the release of radiation into the ocean.
China and South Korea have criticised TEPCO's decision to pump radioactive water into the sea, a process it has now stopped.
There have been contamination fears among Japan's neighbours but China said the impact there had been small and that the radiation was just one per cent of what it had experienced from Chernobyl.
"Its impact on our country's environment has been small, equivalent to about one per cent of the impact of the Chernobyl nuclear accident on our country," China's nuclear safety body said.
"There is no need to adopt protective measures."