Eight people have been confirmed killed after a massive 8.9-magnitude quake hit northeast Japan, causing a four-metre tsunami along parts of the country's coastline.
Japan's NHK television reported many injuries and showed pictures of major tsunami damage in the north, with cars, trucks and houses being swept away in Onahama city in Fukushima prefecture following the quake on Friday.
Police said at least one person was killed in a house collapse in Ibaraki prefecture. Seven other deaths were reported in three other prefectures.
The prime minister said in a televised address that the government was making "every effort possible" to minimise damage.
"The earthquake has caused major damage in broad areas in northern Japan," Naoto Kan said.
"Some of the nuclear power plant in the region have automatically shut down, but there is no leakage of radioactive materials to the environment."
A 10-metre tsunami hit Sendai airport in the north-east. Television footage showed people standing on the roof of the terminal building.
The tsunami roared over embankments in Sendai city, washing cars, houses and farm equipment inland before reversing directions and carrying them out to sea. Flames shot from some of the houses, probably because of burst gas
Military airplanes were flying over the worst-affected areas to assess the need for rescue efforts and an emergency cabinet meeting was held.
Many people were reported injured after a roof caved in during a school graduation ceremony at a hall in east Tokyo, the fire department in the capital said, after the quake hit.
Yukiko Shimahara, a Japanese journalist, told Al Jazeera that the airports and trains in Tokyo have been shut down following the quake.
Meanwhile, a huge fire engulfed an oil refinery in Iichihara near Tokyo, where four million homes were said to be without electricity. Plumes of smoke rose from at least 10 locations in city.
The quake that struck at 2:46pm was followed by a series of powerful aftershocks, including a 7.4-magnitude one about 30 minutes later.
Al Jazeera's Melissa Chan, reporting from Beijing, said tremors were felt as far away as the Chinese capital.
Japan's meteorological agency warned that a tsunami as high as six to 10 metres could strike the coast near Miyagi prefecture, closest to the epicentre and the US Geological Survey issued a tsunami warning for the entire Pacific coast of Japan.
The Pacific Tsunami Warning Center in Hawaii has widened its tsunami warning to cover most of the Pacific Ocean, including Russia, the Philippines, Papua New Guinea, Hawaii, Australia, New Zealand and the Pacific coast of South America but does not include North America.
Al Jazeera's Marga Ortigas, reporting from Manila in the Philippines, said the military there had been ordered to help evacuate areas at risk on the east coast.
Several earthquakes have hit the region in recent days, including a 7.2-magnitude quake on Wednesday.
"Japan has been on high alert since the earthquake on Wednesday," Al Jazeera's Harry Fawcett, following developments from the Malaysian capital, Kuala Lumpur, said.
"Japan is very well equipped to deal both with the initial tremors caused by an earthquake: buildings are systematically built with allowances for sway so that they are less likely to fall down. Also coastal cities have long had tsunami protection measures in place."
Friday's quake struck at a depth of 24 kilometres, about 125 kilometres off the eastern coast, the country's meteorological agency said.
The quake was the biggest in 140 years. It surpasses the Great Kanto quake of 1923, which had a magnitude of
7.9 and killed more than 140,000 people in the Tokyo area.
Japan lies on the "Ring of Fire"- an arc of earthquake and volcanic zones that stretches around the Pacific Rim and where about 90 per cent of the world's quakes occur.