A powerful earthquake has struck off Japan's north-eastern coast, shaking buildings in Tokyo and forcing people out of their homes, witnesses said.
Japan issued its most serious tsunami warning, saying a wave as high as 6m (20ft) could strike the coast near Miyagi prefecture.
US officials said the 8.8-magnitude quake struck about 250 miles (400km) from Tokyo at a depth of 20 miles.
TV pictures showed a wave crashing into the Pacific coast.
The surge of water carried cars and ships as it surged through a coastal town.
Japanese television has shown major tsunami damage in northern Japan, following an earthquake that has been upgraded to 8.8.
Public broadcaster NHK showed cars, trucks, houses and buildings being swept away by the tsunami in Onahama city in Fukushima prefecture.
Scores of cars were seen floating in Iwate prefecture harbour, local TV said.
Japan earlier issued its top tsunami warning in response to the major offshore earthquake, which strongly swayed buildings 400 kilometres away in Tokyo and sent people fleeing onto the streets.
The meteorological agency issued its top-level evacuation alerts for the entire Japanese coast, Russia and the Mariana Islands, the Pacific Tsunami Warning Centre said.
The quake was initially measured as a magnitude 7.9 but was upgraded.
It warned of a tsunami of up to six metres. Smaller tsunamis of up to 50cm reached some coastal communities, the agency said.
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The quake struck about 382km northeast of Tokyo, offshore, the US Geological Survey reported.
Smoke could be seen rising from a building in Tokyo port.
Shinkansen bullet trains stopped when the quake struck, while Tokyo port has shut all 19 of its water gates as it prepares for the tsunami.
Japan’s Coast Guard is halting ships on their way to entering Tokyo’s port,said Takashi Mifune, spokesman for the Bureau of Port and Harbor of the Tokyo Metropolitan Government.
Japan’s meteorological agency said the quake struck at 2.46pm (4.46pm AEDST) local time at a depth of 10km, 125km off the eastern coast.
Footage on national broadcaster NHK from their Sendai office showed employees stumbling around and books and papers crashing from desks.
Police and coast guard officials said they were assessing possible damage from the quake.
The yen tumbled against the dollar after the quake, falling to 83.30 against the dollar from 82.81 before the quake struck.
Several quakes had hit the same region in recent days, including a 7.3 magnitude one on Wednesday.
The Joint Australian Tsunami Warning Centre said there was no tsunami threat to Australia.