An earthquake measuring 8.9 on the Richter scale rocked Japan today, unleashing a 33ft (10m) tsunami which swept boats, cars, buildings and tons of debris miles inland.
At least 20 people died in what was reported to be the biggest earthquake in the world for 140 years. The death toll is expected to rise quickly.
Fires triggered by the quake burned out of control along the north-east coast as more massive aftershocks were felt.
There were reports of several injuries in Tokyo, hundreds of miles away, where buildings shook violently.
TV footage showed waves of muddy water sweeping over farmland near the city of Sendai, carrying buildings, some on fire, inland as cars attempted to drive away.
"This is a rare major quake, and damages could rise by the minute," said Junichi Sawada, an official with Japan's Fire and Disaster Management Agency.
Officials were trying to assess damage, injuries and deaths but had no immediate details.
Police said at least one person was killed in a house collapse in Ibaraki, just north-east of Tokyo.
A large fire erupted at the Cosmo oil refinery in Ichihara city in Chiba near Tokyo and was burning out of control.
Public broadcaster NHK showed footage of a large ship being swept away by the tsunami and ramming into a breakwater in Kesennuma city in Miyagi.
Similar destruction was seen in dozens of communities along the coast.
Footage showed massive damage from the tsunami, with cars, boats and even buildings being carried along by water.
The quake struck at 2.46pm local time and was followed by five powerful aftershocks within about an hour, the strongest measuring 7.1.
The US Geological Survey upgraded the strength of the first quake to a magnitude 8.9, while Japan's meteorological agency measured it at 8.4.
In downtown Tokyo, large buildings shook violently and workers poured into the street for safety. TV footage showed a large building on fire and bellowing smoke in the Odaiba district of Tokyo.
In central Tokyo, trains were stopped and passengers walked along the tracks to platforms. NHK said more than four million buildings are without power in Tokyo and its suburbs.
The ceiling in Kudan Kaikan, a large hall in Tokyo, collapsed, injuring an unknown number of people, NHK said. Osamu Akiya (46) was working in Tokyo at his office in a trading company.
It sent bookshelves and computers crashing to the floor, and cracks appeared in the walls.
"I've been through many earthquakes, but I've never felt anything like this," he said. "I don't know if we'll be able to get home tonight."
Footage on NHK from its Sendai office showed employees stumbling around and books and papers crashing from desks.
It also showed a glass shelter at a bus stop in Tokyo destroyed by the quake and a weeping woman nearby being comforted by another woman. Thirty minutes after the quake, tall buildings were still swaying in Tokyo and mobile phone networks were not working.
The meteorological agency issued a tsunami warning for the entire Pacific coast of Japan.