TOKYO, Oct 23: An earthquake with a magnitude of 6.8 and several powerful aftershocks rocked northern Japan on Saturday, killing at least four people and injuring more than 400 while knocking out power and phone services, media said.

Several houses collapsed and a bullet train was partially derailed by the tremors centred in Niigata prefecture, a rural, mountainous area some 250km north of Tokyo.

In addition to the dead, five people had been buried alive, Kyodo news agency reported as aftershocks continued more than five hours after the initial jolt at 5:56pm (0156pm PST).

That tremor, as well as aftershocks of up to magnitude 6.3, also shook buildings in Tokyo but there were no reports of injuries or damage in the capital.

At least four people were killed in the Niigata area, a rice-growing region on the Sea of Japan, while more than 400 had been injured, media reports said.

"Roads caved in at many locations ... The city is hit by a power outage and traffic lights are off," Shigeru Shinata, an official in Ojiya, a town of about 40,000 where much of the damage appeared to be centred, told national broadcaster NHK.

About 12,000 people had evacuated to schools and other public facilities in Nagaoka, a city of about 200,000, public broadcaster NHK said. Several fires broke out in the city but most were extinguished quickly, media said.

NHK said a landslide had buried three cars and Jiji news agency said an expressway tunnel had collapsed.

Two cars of the bullet train derailed near Nagaoka, but there were no injuries, a Transport Ministry official said.

The focus of the initial quake was about 20 km below the earth's surface.

The government set up a crisis centre in Tokyo, and officials said they were worried about more landslides in areas lashed recently by heavy rains.

Japan has been hit by a record 10 typhoons this year, including one that killed at least 80 people this week.

The quakes were the strongest to hit the region since 1933, officials said.

POWER OUTAGES: Some 278,000 homes were without power and telephone service was disrupted in some areas, making it difficult to contact ambulances to take the injured to hospital, media said.