TOKYO (Reuters) - Power had been restored to almost all customers in the northern Japanese island of Hokkaido by early Saturday, two days after an earthquake caused an island-wide blackout and killed at least 21 people.

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But the impact of Thursday’s 6.7 magnitude quake was set to rumble on with Toyota Motor planning to halt operations at 16 of 18 domestic full-assembly plants due to a parts factory shutdown.

Chief Cabinet Secretary Yoshihide Suga said the confirmed death toll was 21, with six people in cardiopulmonary arrest - a term used in Japan to describe a victim’s condition before death is officially confirmed - and 13 people were missing.

The earthquake triggered landslides that buried houses and paralyzed Hokkaido with widespread power and transport cuts, the latest natural disaster to hit Japan after typhoons, floods and deadly heat waves in the past two months.

Toyota Motor said it would suspend work at the 16 plants on Monday due to the shutdown of its transmission factory in Tomakomai in Hokkaido following the quake.

The company said it would decide later on whether to extend the shutdowns beyond Monday.

Suga called on businesses and Hokkaido’s 5.3 million residents to save power by about 10 percent from Monday, when usage rises, and said the government would likely resort to rolling blackouts if demand threatened to exceed supply capacity.

That would be the first use of rolling blackouts in Japan to deal with power shortages since March 2011, when a magnitude 9 earthquake and tsunami caused the Fukushima nuclear disaster.

Hokkaido Electric said power supplies had been restored island-wide to 2.93 million customers by early Saturday, leaving only 20,000 customers without electricity.

The utility will have supplies of up to 3.6 GW available by the end of Saturday, the trade ministry said, which is still short of pre-quake peak demand of 3.8 GW.

Japanese refiner Idemitsu Kosan Co is preparing to resume truck product shipments at its 150,000 barrels-per-day Hokkaido refinery, a company official said.

Refining operations have been halted since Thursday.