Experts warn of powerful aftershocks in Japan

An aftershock rattled Japan's Hokkaido island yesterday, as experts said more powerful tremors were likely to strike the region after it was battered by a strong earthquake that injured nearly 600 people.

A government team visited the earthquake-prone region to assess damage from powerful earthquakes that struck at dawn on Friday with an initial tremor of 8.0 on the Richter scale - stronger than some killer quakes that have hit the country.

Aftershocks powerful enough to cause heavy damage in the northern region were highly possible, seismologists said.

"Although the number of tremors has been declining, there is a high possibility of strong aftershocks striking the region," said an official at Japan's Meteorological Agency.

"There is a 70 per cent chance that aftershocks with magnitude of six or higher could hit the region in the next three days," he said.

There was a 20 per cent possibility of aftershocks with magnitude of seven or stronger in the next three days, he said.

Friday's earthquake had injured at least 572 people, destroyed or caused heavy damage to 77 homes and forced about 13,000 people to flee from their homes, police said.

At 5.06 p.m. (10.08 a.m.) yesterday, an aftershock measuring 5.2 on the Richter scale struck the region, but there were no immediate reports of damage.

About 300 police, fire and coastguard personnel were searching for two men who were fishing by a river when Friday's quake struck, police said. The two may have been swept away by tidal waves.

Quake-generated waves about one metre high struck the east Hokkaido coast but no major wave damage was reported. Tidal wave, or tsunami, warnings issued immediately after the initial earthquake were lifted on Friday evening.

In 1993, a tsunami caused by a quake measuring 7.8 killed about 200 people on an island off western Hokkaido.

The latest earthquake follows one measuring 6.2 on the Richter scale that hit the northeastern Miyagi prefecture in July, injuring about 500 people. Miyagi was also struck by an estimated 7.0 earthquake in May that injured more than 100.

Tsuneo Katayama, a seismologist and president of the National Research Institute for Earth Science and Disaster Prevention, said the Friday quake was unlikely to trigger larger ones.

He said it was not particularly significant that there had been three earthquakes in northern Japan since May.

Japan is one of the world's most seismically active areas, with an earthquake occurring every five minutes.

Hokkaido, about the size of Austria, is the second largest of Japan's four main islands and has a population of more than five million. The capital, Sapporo, hosted the 1972 Winter Olympics.

Memories are still vivid in Japan of an earthquake in the western city of Kobe that killed more than 6,400 people eight years ago. That quake measured 7.2 on the Richter scale.

The Great Kanto earthquake of September 1, 1923, measured 7.9 on the Richter scale and killed more than 140,000 people in Tokyo and the neighbouring port city of Yokohama.

The last quake of 8.0 or higher in Japan was in 1994.