The quake sparked a fire at an oil depot

The quake, which hit at about 0450 local time on Friday (1950GMT Thursday), sparked a fire at an oil depot, shook buildings and derailed a train.

The main tremor was of force eight, making it the most powerful quake in the world this year, and was followed by two slightly smaller aftershocks.

However, experts said the damage was slight relative to its intensity, because it struck far offshore and was strongest in underpopulated areas.

As most people were asleep when the quake hit, almost all the injuries were caused by falling objects or broken glass in their homes, and so far only two people are said to be seriously hurt.

"Everything was falling over in the house," one man told NHK television. "Something hit my wife on the back."

One 70-year-old woman broke her leg as she tried to flee her house through a window.

The only death related to the quake came when a car hit a man sweeping up broken bottles in the street.

Tsunami alert

Many people were surprised at the strength of the tremor, which was centred 100 kilometres (60 miles) off the eastern coast of Hokkaido.

"We have small quakes here from time to time, but this was completely different," said Eri Takizawa, a local official In Kushiro.

"We felt it shake for a very long time," said Hiroaki Tanaka, a fire official in the town.

The earthquake prompted an automatic shutdown of the Tomato-Atsuma thermal power station in Atsuma and caused a blackout in nearby communities, Kyodo news agency reports.

People woke to find chaos in homes and shops

A fire started at an oil storage depot in Tomakomai, but no one was injured and the fire was brought under control within three hours.

A local train carrying 39 people was derailed, but only one person was injured.

A number of roads were blocked by landslides, and Kushiro airport was temporarily closed after the ceiling of the control tower fell in.

The Japanese authorities have warned local residents to avoid coastal areas due to the possibility of tsunami.

The warning was later down-graded to an alert, a risk which could continue for several days.

Waves of up to 1.2 metres (four feet) were observed in some coastal cities, NHK television network reported.

Even the houses of the dead were damaged

Hokkaido is Japan's northernmost island, with a population of more than five million and is home to a nuclear reactor and active volcanoes.

The capital, Sapporo, hosted the Winter Olympics in 1972.

In January 1995, an earthquake struck the western city of Kobe, killing more than 6,000 people.

Most died of exposure or asphyxiation after being trapped under rubble.

Japan is one of the world's most earthquake-prone countries.

It lies across four slabs of rock, known as tectonic plates, which, when they rub against each other, cause earthquakes.

Experts believe Tokyo, which sits on a different fault line to Hokkaido, is overdue a strong earthquake.