A massive 8.8-magnitude earthquake struck Japan at 2:46pm (12.46pm local time) today unleashing a powerful tsunami that sent ships crashing into the shore and carried cars through the streets of coastal towns.
Multiple injuries, but no immediate deaths, were reported from the Pacific coastal area of Miyagi on the main Honshu island, police said according to media, and TV footage showed widespread flooding in the area.
The quake shook buildings in greater Tokyo, the world's largest urban area with 30 million people.
At least six fires were reported in Tokyo, where the subway system stopped, sirens wailed and people streamed out of buildings.
The first quake struck about 382 kilometres (237 miles) northeast of Tokyo, the US Geological Survey said, revising the magnitude from an earlier 7.9.
Japan, is located on the "Pacific Ring of Fire" and dotted with volcanoes, and Tokyo is situated in one of its most dangerous areas.
A tsunami warning was issued for Japan, Taiwan, Russia and the Mariana Islands, the Pacific Tsunami Warning Center said.
"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.
It also put the territories of Guam, the Philippines, the Marshall Islands, Indonesia, Papua New Guinea, Nauru, Micronesia and Hawaii under a lower tsunami watch.
The government's Earthquake Research Committee warns of a 70 per cent 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.
More recently, the 1995 Kobe earthquake killed more then 6,400 people.