A series of planned electricity blackouts will begin rolling through regions in most of eastern Japan on Monday. The blackouts are intended to manage a dramatic fall in power generation capacity caused by a massive earthquake and tsunami that hit the country.

The quake, the world's fourth largest ever recorded, caused several nuclear power stations to automatically shut down. A subsequent tsunami further damaged some of the plants and led to problems in at least two reactors. As a result, Tokyo Electric Power Co has lost about 27 percent of its electricity generation capacity and will be short of demand by about 10 million kilowatts, it said.

The blackouts will affect outlying areas of Tokyo and regions surrounding the capital, but will not hit central Tokyo. Each will last 3 hours and they will begin in stages from 6:20am and run until 10pm every day. The government warned they could go on for several weeks.

The number of dead and missing stands at around 3,000, but that figure is growing by the hour. A police official in Miyagi prefecture, northern Japan, told public broadcaster NHK on Sunday that he expects the death toll in his region alone to surpass 10,000.

Japan's Meteorological Agency upgraded its assessment of the quake from magnitude 8.8 to 9.0. The quake was actually three very large earthquakes in quick succession, it said Sunday.

The scale of the disaster is huge and its effect on companies and the national economy is difficult to determine. Several electronics companies have plants in the region and they've been offline since Friday.

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Toshiba makes microprocessors and image sensors in the region and its factory has been without power most of the weekend, said Keisuke Ohmori, a spokesman for the Tokyo-based company. "We don't know when we can resume production," he said.

Sony operates several plants in the region and has yet to release information on when they might restart production.

Several companies have announced plans to temporarily suspend production at some domestic factories. They include Toshiba, Panasonic and Sharp. The factories are either impacted by the earthquake or unable to get components because of disruptions to their supply chain.

"This is the worst crisis in Japan's 65-year postwar history," said Prime Minister Naoto Kan. "I'm sure that we will be able to overcome the crisis."

Rescue teams from around the world are pouring into Japan and charities have begun raising money for those affected. Sony and Panasonic each said they would donate ¥300 million (£2.2 million) to relief efforts. Sony said it would also provide 30,000 radios to those affected.