* Fukushima disaster came after tsunami knocked out back-up power

* Restoring full power to island may take a week - minister (Recasts throughout, adds comment)

TOKYO, Sept 6 (Reuters) - Power was restored to a nuclear energy plant in Hokkaido, northern Japan on Thursday after a strong earthquake left it relying on emergency generators for 10 nervous hours, but it may be a week before lights are back on all over the major island. The Japanese national broadcaster NHK is reporting that 125 people have been injured and about 20 are feared missing after a powerful quake triggered dozens of landslides in heavily forested mountains on the northern main island of Hokkaido. A Hokkaido Electric spokesman said the utility was not receiving any supplies from the island of Honshu to the south - home to Tokyo, Osaka and Nagoya - despite there being a 600 megawatt connection for transferring power from the coast of Japan’s main island. Economy, Trade and Industry Minister Hiroshige Seko initially instructed utility officials to restore power at the Tomato Atsuma thermal plant “within a few hours.” But Seko says the plan is now impossible due to damage. TOKYO (Reuters) - After an earthquake knocked out power to 5.3 million people this week, Hokkaido Electric expects to restore service to most of them by the end of Friday, but experts say the island-wide outage highlights fundamental flaws in Japan’s power grid. Kyodo/via REUTERS

Graphic: Earthquake in Hokkaido - tmsnrt.rs/2oJz6zd

The blackout that hit Japan’s northern island of Hokkaido after early Thursday’s quake was the nation’s worst in seven years, but it would have been less extensive if the utility was not so reliant on one large power station, had spread its plants more widely, and could transfer power more easily from other areas, specialists and energy executives said. The outage began at about 7:30 a.m. and a text notification sent out a short time later to affected customers said the outage was “caused by power lines.” The text also stated that 1,224 customers had been affected as of 9:07 a.m., though Paige Sheehan, a spokesperson for Duke Energy, said the number of affected customers is around 5,200.
Energy specialists and executives say a power outage from the earthquake could have been lessened if Hokkaido Electric did not rely so exclusively on the Tomato-Atsuma coal plant. The company has restored electricity to just over half of its affected customers.