Rescuers were rushing to unearth survivors and restore power today after a powerful earthquake jolted Japan's northernmost main island of Hokkaido, buckling roads, knocking homes off their foundations and causing entire hillsides to collapse.

Residents in Sapporo were shaken from their beds when the magnitude 6.7 earthquake struck southern Hokkaido at 3:08am.

At least seven people were confirmed dead, Chief Cabinet Secretary Yoshihide Suga told a news conference. About 30 people were unaccounted for, disaster officials said.

Houses are destroyed by a landslide after the earthquake in Atsuma town, Hokkaido. Photo / AP
Houses are destroyed by a landslide after the earthquake in Atsuma town, Hokkaido. Photo / AP
Police search for missing persons around a house destroyed by a landslide. Photo / AP
Police search for missing persons around a house destroyed by a landslide. Photo / AP
Trees toppled down on houses after a landslide caused by a powerful earthquake in Atsuma town. Photo / AP
Trees toppled down on houses after a landslide caused by a powerful earthquake in Atsuma town. Photo / AP

Video cameras showed cities going dark as the quake disabled power systems, leaving nearly 3 million households on the island without electricity.

Advertisement

The island's only nuclear power plant, which was offline, switched to a backup generator to keep its spent fuel cool and nuclear regulators said there was no sign of abnormal radiation — a concern after a massive quake and tsunami in March 2011 that hit northeast Japan destroyed both external and backup power to the Fukushima Dai-ichi nuclear plant, causing meltdowns.

Japan's Meteorological Agency said the quake's epicenter was 40km deep. But it still wreaked havoc across much of the relatively sparsely inhabited island.

Rescuers were using small backhoes and 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 and leaving scores of brown gashes in the deep green hills.

Airports and many roads on the island were closed and trains were idled by the power outages.

Buildings destroyed by a landslide block a road after an earthquake in Atsuma town, Hokkaido. Photo / AP
Buildings destroyed by a landslide block a road after an earthquake in Atsuma town, Hokkaido. Photo / AP
A police officer checks around buildings destroyed by a landslide after the quake. Photo / AP
A police officer checks around buildings destroyed by a landslide after the quake. Photo / AP
Police search for missing people around houses destroyed by a landslide. Photo / AP
Police search for missing people around houses destroyed by a landslide. Photo / AP
Police continue to search for missing people at the site of a landslide after an earthquake in Atsuma town. Photo / AP
Police continue to search for missing people at the site of a landslide after an earthquake in Atsuma town. Photo / AP

NHK showed workers rushing to clean up shattered glass and reinstall ceiling panels that had tumbled down in the region's biggest airport at Chitose.

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

The quake came on the heels of a typhoon that lifted heavy trucks off their wheels and 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.

This aerial photo shows the extent of the landslide after the quake hit. Photo / AP
This aerial photo shows the extent of the landslide after the quake hit. Photo / AP

As Japan's northern frontier and a major farming region with rugged mountain ranges and vast forests, Hokkaido is an area accustomed to coping with long winters, isolation and other hardships.

But the blackouts brought on by the quake underscored the country's heavy reliance on vulnerable power systems: without electricity, water was cut to many homes, train lines were idled and phone systems out of order.

In the prefectural capital of Sapporo, a city of 1.9 million, the quake ruptured roads and knocked houses askew.

A mudslide left several cars half buried.

Cars are stuck in a mud-covered road after an earthquake in Sapporo, Hokkaido. Photo / AP
Cars are stuck in a mud-covered road after an earthquake in Sapporo, Hokkaido. Photo / AP
Cars sit on a road damaged by an earthquake in Sapporo, Hokkaido. Photo / AP
Cars sit on a road damaged by an earthquake in Sapporo, Hokkaido. Photo / AP
A cracked road and destroyed buildings are seen after the earthquake in Atsuma town. Photo / AP
A cracked road and destroyed buildings are seen after the earthquake in Atsuma town. Photo / AP

By late Thursday, stores were closed and the city's streets were deserted.

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

The hope had been to get power back up within hours and some electricity was gradually being restored.

However, damage to generators at the Tomato Atsuma plant meant that a full restoration of power could take more than a week, Seko said.

He said utilities were starting up several other thermal and hydroelectric plants but even with those stopgap supplies thousands would still be without power for some time.

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.

The quake's impact was widespread. To the north, in the scenic town of Biei, residents lined up outside of supermarkets and convenience stores, quickly clearing shelves of water, toilet paper and food.

"Only a few cartons of instant ramen were left," said Mika Takeda, who lives in the town of 10,000.

The one local gas station was limiting customers to only 20 litres of gas, she said.

-AP