At least 32 people were killed and many injured after a powerful 8.9-magnitude earthquake struck off Japan's northeastern coast Friday, triggering a tsunami as high as 10 metres.

Japan's National Police Agency and officials said at least 32 people were killed, including 10 in Iwate Prefecture by tsunami waves, Kyodo News said.

The US Geological Survey said the epicenter was about 250 miles from Tokyo at a depth of 20 miles. They earlier estimated the quake to be of 7.9 in magnitude but later revised it to 8.9 on Richter scale.

The earthquake has caused major damage in broad areas in northern Japan, Prime Minister Naoto Kan said.

Our initial assessment indicates that there has already been enormous damage, chief government spokesman Yukio Edano said. We will make maximum relief effort based on that assessment.

The tremors were felt all over Japan including Shizuoka-ken where houses swayed for two to three minutes, while the local TV channels showed fires in some places.

Japan is one of the world's most seismically active areas and accounts for about 20 percent of the world's earthquakes of magnitude 6 or greater. The country's worst previous quake was in 1923 in Canto that killed more than 140,000 people.

Around 20 countries and numerous Pacific islands have been issued tsunami warning after the powerful earthquake, the National Weather Service said.

Meanwhile, four nuclear power plants closest to Friday's powerful 8.9-magnitude earthquake that struck off Japan's northeastern coast have been safely shut down, the International Atomic Energy Agency (IAEA) said.