A massive 8.9-magnitude earthquake hit northeast Japan Friday, setting a nuclear plant ablaze, unleashing a 10-metre tsunami that tossed ships inland and a deathtoll of at least 40 people.
It was the strongest earthquake ever to hit Japan. Police said many others were injured in Tokyo and coastal areas of the main Honshu island while television footage showed scenes of utter devastation and flooding.
A monster 10-metre (33 feet) tsunami wave hit near Sendai city where a tide of black water sent shipping containers, cars and debris crashing through streets and across open farmland destroying everything in its path.
The government said the tsunami and quake, which was felt as far away as Beijing, some 2,500 kilometres (1,500 miles) away had caused "tremendous damage" while aerial footage showed massive flooding in northern towns.
"I've never seen anything like this," said Ken Hoshi, a local government official in Ishinomaki, a port city in Miyagi prefecture.
The quake was the largest ever to hit Japan, the fifth strongest tremor worldwide since 1900 and the seventh strongest in history, according to the US Geological Survey and Japanese seismologists.
The Pacific Tsunami Warning Centre issued a widespread warning for territories as far away as South America, New Zealand and Hawaii, where people were ordered to evacuate coastal areas.
"An earthquake of this size has the potential to generate a destructive tsunami that can strike coastlines near the epicentre within minutes and more distant coastlines within hours," the centre said in a statement.
But fears of the tsunami wreaking destruction across the Pacific Ocean subsided after waves hit Russia and Taiwan without causing any major damage.
Television footage showed a wide, muddy tide moving rapidly across a residential area near the Natori River in Sendai. Public broadcaster NHK said several dozen houses had been washed away in Miyagi Prefecture.
The tsunami also reached Sendai airport, submerging the runway while a process known as liquefaction, caused by the intense shaking of the tremor, turned parts of the ground to liquid.
A fire broke out in the turbine building of Onagawa nuclear plant in Miyagi Prefecture on Friday, Kyodo News reported. It was not known if there was any immediate threat of radioactive leak.
The government had earlier tried to reassure people that there was no danger of a leak from the country's network of nuclear power plants.
In the capital, where millions evacuated strongly swaying buildings, multiple injuries were reported when the roof of a hall collapsed during a graduation ceremony, police said.
Plumes of smoke rose from at least 10 locations in the city, where four million homes suffered power outages. An oil refinery was ablaze near Tokyo.
The first quake struck just under 400 kilometres (250 miles) northeast of Tokyo, the US Geological Survey said. It was followed by more than a dozen aftershocks, one as strong as 7.1.
"We were shaken so strongly for a while that we needed to hold on to something in order not to fall," said an official at the local government of the hardest-hit city of Kurihara in Miyagi prefecture.
"We couldn't escape the building immediately because the tremors continued... City officials are now outside, collecting information on damage," she told AFP by telephone.
A major blackout occurred across a wide area of northeastern Japan.
Prime Minister Naoto Kan quickly assembled his cabinet after the quake hit, and the government dispatched naval vessels from near Tokyo to Miyagi.
The quake affected the nation's key transportation systems, including Narita airport, which shut its runways for safety checks.
The quake, which hit at 14:46 pm (0546 GMT) and lasted about two minutes, rattled buildings in greater Tokyo, the world's largest urban area and home to some 30 million people.
In Tokyo, where the subway system stopped, sirens wailed and people streamed out of buildings.
Japan sits on the "Pacific Ring of Fire", which is dotted with volcanoes, and Tokyo is situated in one of its most dangerous areas.
The quake sent the Nikkei share index plunging at the close while the yen fell sharply against the US dollar before recovering.
The mega-city of Tokyo sits on the intersection of three continental plates -- the Eurasian, Pacific and Philippine Sea plates -- which are slowly grinding against each other, building up enormous seismic pressure.
The government's Earthquake Research Committee has warned of a 70 percent chance that a great, magnitude-eight quake will strike within the next 30 years in the Kanto plains, home to Tokyo's vast urban sprawl.
The last time a "Big One" hit Tokyo was in 1923, when the Great Kanto Earthquake claimed more than 140,000 lives, many of them in fires. In 1855, the Ansei Edo quake also devastated the city.
In 1995 the Kobe earthquake killed more than 6,400 people.
More than 220,000 people were killed when a 9.1-magnitude quake hit off Indonesia in 2004, unleashing a massive tsunami that devastated coastlines in countries around the Indian Ocean as far away as Africa.
Small quakes are felt every day somewhere in Japan and people take part in regular drills at schools and workplaces to prepare for a calamity.
Nuclear power plants and bullet trains are designed to automatically shut down when the earth rumbles and many buildings have been quake-proofed with steel and ferro-concrete at great cost in recent decades.