The devastating 8.9-magnitude quake left many people injured in coastal areas of the main Honshu island and Tokyo, police said, while TV footage showed widespread flooding in the area. Nineteen people were reported dead.

A monster 10-metre (33 feet) wall of water was reported in Sendai city in northeastern Miyagi prefecture, media said after a four-metre wave hit the coast earlier. The government said the quake had caused "tremendous damage".

Helicopter footage showed massive inundation in northern coastal towns, where floods of black water sent shipping containers, cars and debris crashing through streets. An oil refinery was ablaze near Tokyo.

The Pacific Tsunami Warning Centre issued a widespread warning for territories as far away as South America, New Zealand and Hawaii, where evacuations were ordered.

"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.

Swells of up to one metre were reported hitting Russia's far east, with bigger waves expected later.

Television footage showed a wide, muddy stream moving rapidly across a residential area near the Natori River in Sendai, levelling all in its path.

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.

Public broadcaster NHK said several dozen houses had been washed away in Miyagi Prefecture.

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.

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.

The quake was the largest ever in Japan, the fifth strongest tremor worldwide since 1900 and the seventh strongest in history, according to the US Geological Survey and Japanese seismologists.

"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. The government moved to reassure people that there had been no radiation leak from the country's network of nuclear power plants.

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 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.

earlier related report
Major tsunamis around the world
Tokyo (AFP) March 11, 2011 - A 10-metre-high tsunami ploughed into the Japanese coast Friday, dashing ships into the shore, washing away houses and leaving devastation in its wake.

The destructive wave, triggered by a massive 8.9-magnitude undersea quake just 130 kilometres (80 miles) off the coast, inundated large areas of farmland in northern Japan and set off Pacific-wide warnings.

Here is a chronology of some of the major quakes and tsunamis around the world since the Asian tsunami of December 2004 which left more than 220,000 dead in what was one of the world's worst natural disasters:

-- December 26, 2004: SOUTHEAST ASIA - A 9.3-magnitude undersea quake off the coast of Sumatra island triggers a tsunami that kills 220,000 people in countries around the Indian Ocean, including 168,000 in Indonesia.

-- July 17, 2006: INDONESIA - A 7.7-magnitude undersea quake strikes off Indonesia's Java island, unleashing a tsunami, killing at least 654.

-- April 2, 2007: SOLOMON ISLANDS - An 8.0-magnitude quake in the Western Solomon Islands triggers a tsunami that kills 52 people and displaces thousands.

-- September 29, 2009: SAMOA - A tsunami sparked by an 8.0-magnitude earthquake flattens villages and resorts in Samoa and the neighbouring Pacific islands of American Samoa and northern Tonga, killing more than 190 people.

-- February 27, 2010: CHILE - An 8.8-magnitude earthquake rocks Chile, killing at least 521 people and leaving 56 missing. Most of the dead are in the coastal area of Maule, 400 kilometres (250 miles) south-west of the capital Santiago.

-- October 25-26: INDONESIA - At least 112 people are killed and over 500 missing after a tsunami unleashed by a powerful 7.7 magnitude quake strikes off the island of Sumatra.

-- March 11: JAPAN - An 8.9 undersea quake triggered a powerful tsunami that smashed into northern Japan. Reports put the size of the wave at as much as 10 metres (33 feet) in the port city of Sendai.

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