Japan’s northern island of Hokkaido began to restore power after a strong earthquake overnight knocked out electricity throughout the entire prefecture of more than 5 million people.

The magnitude 6.7 quake that hit on the western part of the island at 3:08 a.m. cut off power to nearly 3 million buildings, and damaged a key thermal plant. One plant was brought back online just before 3 p.m. local time, restoring power to some areas after almost 12 hours of blackouts. Fully restoring electricity throughout the region could take more than a week, Economy Minister Hiroshige Seko told reporters.

Seven people were confirmed dead, Chief Cabinet Secretary Yoshihide Suga said. The quake destroyed multiple buildings and caused landslides, and television footage showed roads ripped apart or liquefied by the shaking. The main New Chitose airport was closed Thursday and all trains on the island are halted.

“While gathering information about the damage as quickly as possible, we will work closely with local authorities and do all in our power to rescue those affected, evacuate local people and restore essential services,” Prime Minister Shinzo Abe told an emergency meeting of ministers.

Hokkaido makes up nearly a quarter of Japan’s land mass, but it is one of the least populated regions. Its scenery and world-class skiing have made it a top destination for tourists, though its economy accounts for only about 3.5 percent of GDP.

Shaking from the quake was the highest possible on the Japanese intensity scale of 7, the JMA said, the same strength as the 2016 Kumamoto quakes that killed more than 250 people, the March 11, 2011 disaster that triggered a tsunami, and the 1995 Kobe quake. The JMA initially rated the quake at the second-highest level.

At least 33 people were missing, with more than 100 injured, national broadcaster NHK said.

Grid Imbalance

The Tomato Atsuma coal-fired power plant was automatically shut off after the quake, causing a grid imbalance which triggered the massive outage. The 1.65 gigawatt plant, which was supplying about half the region’s power at the time of the quake, was damaged and restoring it will take at least a week, Seko said.

To re-balance the grid and end the blackout, Hokkaido Electric Power Co. restarted the No. 1 unit at the Sunagawa coal-fired facility which resorted power to limited areas. Seko called for residents to use as little electricity as possible.

The utility aims to have about 2.9 gigawatts of generation online by Friday, Seko said — not enough to meet the island’s peak demands. Blackouts may be extended in some areas, and hospitals and other important facilities will be prioritized, he said. Power lines connecting Hokkaido to the main island of Honshu are offline, which means that Hokkaido can’t receive power from neighboring utilities.

External power to the Tomari nuclear plant was initially cut off, though emergency generators kicked in at the facility which has been offline since 2012. Power has now been restored to the facility.

Shares in Hokkaido Electric closed down 6.4 percent, the most in almost two years. The utility also delayed a planned sale of bonds.

Shares Halted

Trading at the Sapporo Securities Exchange was called off for the day due to the power outage, Japan Exchange Group said, with no decision yet made on trading Friday. The regional bourse is the only exchange on which Rizap Group Inc., a gym operator with a market value of more than $3.5 billion, is listed.

Earlier in the week, a powerful typhoon struck western Japan around Osaka, killing at least 10 people. Kansai International Airport, the region’s main air hub, is still closed after the storm flooded runways and a tanker smashed into the bridge connecting the airport to the mainland. The airport aims to resume some operations Friday.