Japanese television showed cars, ships and even buildings being swept away by a vast wall of water after the 8.9 magnitude earthquake.
The quake has sparked fires in several areas including Tokyo, and numerous casualties are feared.
It struck about 250 miles (400km) from the capital at a depth of 20 miles. There have been powerful aftershocks.
The tremor at 1446 local time (0546 GMT). Seismologists say it is one of the largest earthquakes to hit Japan for many years.
The tsunami warning was extended to the Philippines, Indonesia, Taiwan, the Pacific coast of Russia and Hawaii.
Map of Japan
Tsunami waves hit Japan's Miyagi and Fukushima prefectures, officials said.
Japan's NHK television showed a massive surge of debris-filled water sweeping away buildings, cars and ships and reaching far inland.
The earthquake also triggered a number of fires, including one at an oil refinery in Ichihara city in Chiba prefecture near Tokyo, engulfing storage tanks.
There were reports of about 20 people injured in Tokyo after the roof of a hall collapsed onto a graduation ceremony.
Bullet train service to northern Japan was halted, rapid transit in Tokyo was suspended and some nuclear power plants automatically shut down.
Prime Minister Naoto Kan said there had been no radiation leaks. "
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OMFG.