Tokyo - Small tsunami waves hit northern and eastern Japan on Saturday after a powerful north Pacific earthquake prompted tsunami warnings across northern and eastern Japan and Russia, as well as Alaska.

Tsunami watches were also issued for parts of the Pacific, a region that is nervous about tsunami two years after a deadly wave off Aceh in Indonesia killed more than 230,000 people. The watches included Guam, Taiwan, the Philippines and Hawaii.

A 40 cm (16 inch) wave was reported at Chichijima in the Ogasawara islands, some 1,200 km south of Tokyo, and several smaller waves on Hokkaido and northern Japan, but there were no reports of injuries and no immediate reports of damage.

Japan later downgraded the tsunami warning to a "watch". It had earlier issued evacuation advisories for tens of thousands of households in the country.

The USGS (U.S. Geological Survey) put the quake magnitude at 7.9, a "major" tremor, and said its epicentre was 525 km (325 miles) east northeast of Kuril'sk, Kurile islands, and 1,710 km (1,065 miles) northeast of Tokyo.

The same area was struck by a powerful quake in November, prompting evacuations and tsunami warnings, but in the end only small waves -- the highest 40 cm -- reached Japan.

An official in Russia's Emergencies Ministry told Reuters that the threat of a tsunami had passed.

"Half-past eight, nine o' clock Moscow time (0530-0600 GMT) was the approximate time the threat of a tsunami was due to appear. That time passed, and the threat did not materialise. Everything is normal," the official said.

Wide Warning

Japan's Meteorological Agency had said that tsunami as high as a metre (yard) could hit parts of Hokkaido and that smaller waves were likely to hit a wide area of Pacific coastal areas from Hokkaido to Wakayama prefecture in western Japan on the country's largest main island of Honshu.

Hokkaido officials urged residents to move to higher ground, and fire trucks made the rounds of coastal areas warning about the possibility of a tsunami. There was only moderate shaking in Hokkaido and no immediate reports of injury due to the quake.

Television footage showed one worried resident of Kushiro studying the coastline with binoculars from an evacuation centre.

"I'm scared to return home," one woman, cradling a child, told NHK.

An official in the Philippines said they had issued a tsunami alert "level one", which warned residents on the northern and eastern coastlines to wait for further information and possible evacuation.

Officials in Taiwan, also included in the Pacific-wide tsunami watch, said they would continue to monitor for several hours but that they did not expect anything to happen.

A tsunami, Japanese for "harbour wave," travels at dizzying speed in the open ocean and, when it approaches shallow water along a coast, slows and swells. In an inlet, it can rise to a towering height very quickly.

In 1993, a tsunami caused by a 7.8 magnitude earthquake killed about 200 people on the island of Okushiri, off Hokkaido's southwestern coast.