"We are looking into the cause and the situation and we'll make that public when we have further information," he said.
Meanwhile, Chief Cabinet Secretary Yukio Edano says the government is collecting iodine, which can be used against radiation sickness.
The forecast is for winds from the westerly quarter for the next several days - which would blow any toxic gas out to sea.
This may indicate that some of the metal containers of uranium fuel may have started melting.
University of Tokyo Professor Naoto Sekimura said it was possible only a small part of the fuel may have melted and leaked outside.
AFP and Japan's NHK TV reported a blast at Fukushima No. 1 atomic plant, 250 kilometres northeast of Tokyo. The Tokyo Electric Power Company - which runs the plant - says four workers were injured.
Public broadcaster NHK showed delayed footage of smoke billowing from the site, also reporting that the reactor building had been destroyed.
The council said 224,243 people were moved off the coasts overnight, either on their own or using military trucks.
Small waves struck the country, but caused no damage or casualties.
The officers are from the Urban Search and Rescue (USAR) contingent, codenamed Operation Lionheart.
Four of them returned from Christchurch on March 6 after participating in search and rescue efforts here.
The official death toll stands at 413, while police said between 200 and 300 more bodies were found along the coast in Sendai, the biggest city in the area near the quake's epicentre.
There are 784 people missing and 1,128 injured.
More than 215,000 people are living in 1,350 temporary shelters in five prefectures, or states, according to national police.
Ryohei Shiomi said officials were checking whether a meltdown had taken place at the Fukushima Dai-ichi power plant, which had lost cooling ability.
Shiomi said that even if there was a meltdown, it wouldn't affect humans within a 10km radius.
Electricity is in short supply after its power facilities were damaged by the earthquake.
TEPCO is asking people to conserve electricity.
Civil Defence says no further tsunami threat exists for New Zealand. Minor fluctuations in sea level may continue for up to 48 hours and caution is required on beaches and in marine environments.
The death toll has reached 398, with the number likely to rise to well over 1,000.
Meanwhile, 805 people remain missing.
The team will be made up of firefighter rescue specialists, supported by two structural engineers, eight paramedics, two doctors, and a police specialist.
Japan's Prime Minister Naoto Kan has inspected a quake-hit nuclear power plant in Fukushima.
"I realised the huge extent of the tsunami damage," Kan told the Kyodo News agency.
He said there were munute amounts of radiation being released from the plant.
The Tokyo Electric Power Co. has warned of power shortages and an "extremely challenging situation in power supply for a while", as several of its nuclear power plants just north of the city remain under close scrutiny.
The Japan tsunami disaster marks a rather macabre milestone in such global events - it's the first one where the world has watched as the disaster unfolds on their TV screens, live. Cameras showed the brown mass of water and debris inundating the town of Sendai and surrounding fields last night, as the event happened.
A strong 6.8-magnitude aftershock has struck off the east coast of Japan, US seismologists said, less than 24 hours after a massive earthquake created a powerful and destructive tsunami.
The aftershock, which the US Geological Survey said hit at a depth of just 24 kilometres, was centred 174km east-southeast of the city of Sendai, the scene of huge devastation when a 10-metre tsunami struck yesterday.
Officials monitoring tidal levels on the coast of Latin America and South America report only small waves coming ashore, following the tsunami near Japan.
The official death toll from Japan's earthquake/tsunami disaster now stands at 402 - but the Kyodo News agency says it estimates that more than 1000 people died.
A number of US Pacific Fleet ships in the Western Pacific, including an aircraft carrier, are converging on Japan to be in the best position to help those in areas damaged by the massive earthquake and subsequent tsunami.
A gallery of dramatic Reuters photos out of Japan here on The Atlantic website.
The ship was owned by a shipbuilder in Ishinomaki, Miyagi prefecture.
Warnings still apply for Japan, Russia, Mexico, French Polynesia, Pitcairn Island, Guatemala, El Salvador, Nicaragua, Antarctica, Panama, Honduras, Chile, Ecuador, Colombia, and Peru.
People should still follow any advisories/warnings from their local authorities.
The New Zealand Tsunami Expert Panel assessment is that there is still a marine and minor land threat only for parts of the upper North Island coasts of New Zealand.
A minor land threat still exists for Northland between Ahipara and the Karikari Peninsula as well as in the Bay of Islands and the Chatham Islands, while a marine threat remains for the northern North Island from Kaipara to Ahipara and south of the Karikari Peninsula, around the Coromandel Peninsula and Bay of Plenty to Gisborne.
Meanwhile, search and rescue teams from the UK - the International Rescue Corps and Rapid UK - say they are on standby having both formally offered their services, the BBC reports.
Japan's nuclear safety agency is also set to order a plant operator of another plant to release slightly radioactive vapor to protect the reactor from damage.
Altogether, five reactor units - two at the Fukushima No. 1 plant and three at nearby Fukushima No. 2 plant - are in a state of emergency. All five plants have shut down.
Officials said earlier that only one of the two Fukushima No. 1 plant's units had cooling problems resulting from power outages. They now say both units are troubled.
Auckland Japanese Society chairman Masa Sekikawa says many have been glued to their TVs since the quake struck.
Tomorrow's planned Japanese Festival in Auckland looks set to be a day of mourning, he said.
"They are both on the same so called Pacific Ring of Fire belt but are so far from one another that it's a very remote possibility that one triggered the other. The Christchurch event was magnitude 6.3, so this magnitude 8.9 one packed about 8,000 times more energy but was much further removed from any urban area, so its effects in terms of ground shaking were milder. The tsunami waves are really one way of transporting the energy released by the earthquake to points farther."
The six will travel to Japan tonight and the balance of a team of 48 would probably leave tomorrow, following a request from Japan, he said this afternoon.
He said 11,000 Australians are understood to be resident in Japan, with "hundreds" estimated by the embassy to be in the affected area, including a large number of language teachers.
Australians looking for information on missing loved ones and Australians in Japan registering with the Australian Government that they are ok, should call the Department of Foreign Affairs and Trade on 1300 555 135.
David Applegate said the quake likely caused "tens of millions of dollars" in structural damage in Japan.
The team, who have been assisting with rescue and recovery operations in Christchurch following the February 22 quake, was planning to leave the city this weekend but brought forward their departure to help with rescue efforts in Japan.
Civil Defence National Controller Steve Brazier thanked the team members for their efforts in assisting with the Christchurch rescue efforts and has sent his condolences to the people of Japan.
Search and Rescue teams from New Zealand have also been requested by Japan, the United Nations says.
At least four teams have been requested by Japan, Elisabeth Byrs, spokeswoman of the UN Office for the Coordination of Humanitarian Affairs; New Zealand, Australia, South Korea and the United States, said.
UN Secretary-General Ban Ki-moon said the UN would do all it could to mobilise humanitarian assistance and disaster risk reduction teams as soon as possible to the earthquake- and tsunami-ravaged areas.
The evacuation order was for "all people living in defined flood zones." He described it as a "preventative" move.
Many of the 524 killed in last year's Chilean earthquake died as a result of a tsunami triggered by the quake.
The amount of radiation has reached around 1000 times the normal level in the control room of the No. 1 reactor of the Fukushima No. 1 nuclear power plant, the Nuclear and Industrial Safety Agency told Kyodo News.
Several people are believed to have been washed out to sea, including one man who was taking photos of the tsunami.
Residents say around 30 boats were crushed in the harbour, with water destroying most of the docks.
Crescent City was hit by a tsunami in 1964 which killed 11 people and destroyed nearly 300 homes and businesses.
The harbour was also hit badly by tsunami-driven currents in 2006, doing US$10m worth of damage.
Tokyo Electric says the amount of air to be released will be small and that it will notify residents near the plant before it starts releasing the air.
The tsunami warning has been downgraded to an advisory in Hawaii, but officials said people should still stay away from beaches.
"First and second wave in [Baya California] were 70 cm. Some experts say that the third wave may be strong and dangerous," he wrote.
Mexico's tsunami alert remains in place.
Far North Civil Defence controller Alastair Wells told Radio New Zealand a surge of around 20cm is expected initially, but this is forecast to build up to 1m within the next three hours.
The tsunami marine warning will remain in place until an all clear is pronounced, Mr Wells said.
The water reportedly dropped by about 9 feet (2.7m) at Santa Cruz's harbour as water was sucked out to sea around 8.10am Pacific Standard Time (5.10am NZST).
Several boats broke loose and part of a dock was also pulled away during one of several surges, each of which took about 10 minutes.
Harbour officials have advised the public to evacuate the area and shelters have been set up along the west coast of the US for residents in the impacted area.
View Magnitude 8.9 earthquake triggers huge tsunami in a larger map
Wave heights of 0.2m have been observed in Nauru and in the Solomon Islands capital of Honiara.
Civil Defence says there is a minor land threat only for parts of the upper North Island coasts of New Zealand.
Based on real-time tsunami modelling and comparison with historical events, the interpretation is that a minor land threat - wave heights of just over 1m - now exists in Northland between Ahipara and the Karikari Peninsula as well as in the Bay of Islands and the Chatham Islands.
Passage of the wave through the South Pacific has been observed, however there is no indication of wave arrival in the Kermadec islands.
It was expected the first wave to arrive at New Zealand would reach North Cape at approximately 6.23am, however monitoring of the propagation of the tsunami across the Pacific indicates that actual arrival times may be approximately an hour later than first indicated.
"I guess you can add about 3000 to the 3500 and that would be about it. But that's just a guess," he said.
Mr Kennedy said with telephones down, authorities are using Skype and Facebook to reach New Zealanders in Japan.
People concerned about friends and family in Japan should contact the Ministry of Foreign Affairs and Trade on 0800 432 111.
"Today's event shows us how fragile life can be," he said.
Mr Obama said one US aircraft carrier was in Japan and another was on the way. He said the US would assist as required by Japan.
The tsunami has hit the US territory of Guam and the state of Hawaii, but Mr Obama said there had been no reported damage in the United States.
Another 137 have been confirmed killed and 531 are missing. Police also said 627 people had been injured.
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