Rescuers are searching for survivors and trying to restore power after a powerful earthquake hit the Japanese island of Hokkaido.

At least seven people are known to have died after the magnitude 6.7 earthquake struck at 3.08am.

The quake disabled power systems, leaving nearly three million households on the island without electricity and left in the dark.

The island’s only nuclear power plant, which was offline, switched to a back-up generator to keep its spent fuel cool, and nuclear regulators said there was no sign of abnormal radiation.

Police search for missing people at the site of a landslide after an earthquake in Atsuma town, Hokkaido. Credit: AP

Japan’s Meteorological Agency said the quake’s epicentre was 24 miles deep but it still wreaked havoc across much of the relatively sparsely inhabited island.

Chief Cabinet Secretary Yoshihide Suga told a news conference that seven people had been confirmed dead.

Rescuers were using shovels to sift through the tons of soil, rocks and timber in hopes of finding survivors in the town of Atsuma, where steep mountainsides collapsed, crushing homes and farm buildings.

Disaster officials in Hokkaido said about 30 people were unaccounted for.

Houses were destroyed by a landslide after an earthquake in Atsuma town, Hokkaido, northern Japan. Credit: AP

Airports and many roads on the island were closed and trains were halted due to power outages.

Japan is used to dealing with disasters but the last few months have brought a string of calamities.

The quake came shortly after a typhoon that triggered heavy flooding in western Japan, leaving the main airport near Osaka and Kobe closed after a tanker rammed a bridge connecting the facility to the mainland.

The summer also brought devastating floods from torrential rains in Hiroshima and deadly hot temperatures across the country.

Prime Minister Shinzo Abe said that up to 25,000 troops and other personnel would be dispatched to Hokkaido to help with rescue operations.

People line up outside a supermarket to buy supplies after an earthquake, in Biei town, Hokkaido. Credit: AP

In the prefectural capital of Sapporo, a city of 1.9 million, the quake ruptured roads and damaged houses - a mudslide also left several cars half buried.

Economy, Trade and Industry Minister Hiroshige Seko told reporters the extensive power outage was caused by an emergency shutdown of the main thermal power plant which supplies half of Hokkaido’s electricity.

The hope had been to get the power back up within hours and some areas restored but damage to generators at the Tomato Atsuma plant meant the restoration of power could take more than a week, Mr Seko said.

In the meantime, authorities sent power-generator vehicles to hospitals and other locations.

Reacting quickly to the disaster, troops deployed water tanker trucks in Sapporo, where residents were collecting bottles to tide them over until electricity and tap water supplies come back online.

The city hall announced it had set up charging stations to help residents charge their mobile phones.