A massive 8.9-magnitude quake has 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.
A 10-metre tsunami hit Sendai airport in the north-east. Television footage showed people standing on the roof of the terminal building and the Kyodo news agency reported that one person had been killed in Sendai.
Military airplanes were flying over the worst-affected areas to assess the need for rescue efforts and an emergency cabinet meeting was under way.
Many people were 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 on Friday.
A huge fire engulfed an oil refinery in Iichihara near Tokyo
Four million homes in Tokyo were said to be without electricity.The quake shook buildings in the capital for several minutes and sent people out onto the streets.
The news agency AFP said multiple injuries, but no immediate deaths, were reported from the Pacific coastal area of Miyagi on the main Honshu island.
Japan's NHK television showed black smoke billowing from a building in Odaiba, a suburb of Tokyo.
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.
Tremors were felt as far away as in the Chinese capital, Beijing.
The country's meteorological agency warned that a tsunami as high as six metres could strike the coast near Miyagi prefecture, closest to the epicentre.
There was a warning of a 10-metre tsunami following the quake, Japan's biggest in 7 years.
The US Geological Survey issued a tsunami warning for the entire Pacific coast of Japan.
The Pacific Tsunami Warning Center in Hawaii said a tsunami warning was in effect for Japan, Russia, Marcus Island and the Northern Marianas. A tsunami watch has been issued for Guam, Taiwan, the Philippines, Indonesia and the
US state of Hawaii.
US state of Hawaii.
An 7.2 earthquake hit Japan on Wednesday.
"Japan has been on high alert since the earthquake on Wednesday," Al Jazeera's Harry Fawcett, following developments from Kuala Lumpur, said
"Japan is very well equipped to deal both with the initial tremors caused by an earthquake: buildings are systematically built with in-built allowances for sway so that they are less likely to fall down. Also coastal cities have long had tsunami protection measures in place."
Yukiko Shimahara, a Japanese journalist, told Al Jazeera that the airports and trains in Tokyo have been shut down following the quake.
Friday's quake struck at a depth of 24 kilometres, about 125 kilometres off the eastern coast, the meteorological agency said.
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.
Several earthquakes have hit the region in recent days, including a 7.2-magnitude quake on Wednesday.