At least two people are known to have died in yesterday's strong aftershock in northeastern Japan.
The aftershock was the strongest tremor since the March 11th earthquake and did some damage, but it did not generate a tsunami and appeared to have spared the area's nuclear power plants.
The Fukushima Dai-ichi complex - where workers have been frantically trying to cool overheated reactors since they lost cooling systems last month - reported no new abnormalities. Other facilities retained a connection to the grid or switched to diesel generators after the 7.1-magnitude quake knocked out power to much of the area.
Many people in the area have lived without water and electricity for nearly a month, and the latest tremor sunk more homes into blackness: In total, around 3.6 million households - about 60 per cent of residents in the area - were left in the dark, said a spokesman for Tohoku Electric Power, which serves northern Japan.
Five conventional plants in the area were out, and it was not clear when power would be restored, he said.
Yesterday's quake initiated a tsunami warning of its own, but it was later cancelled. Two people were killed, fire department spokesman Junichi Sawada reported today. A 79-year-old man died of shock and a woman in her 60s was killed when power was cut to her oxygen tank. More than 130 people were injured, according to the national police agency.
The quake epicentre was in about the same location as the original 9.0-magnitude tremor, off the eastern coast and about 65km from Sendai, an industrial city on the eastern coast, according to the US Geological Survey. It was strong enough to shake buildings for about a minute as far away as Tokyo, about 330km away.
The operator of the tsunami-ravaged Fukushima Dai-ichi plant said there was no sign the aftershock had caused new problems there. Workers briefly retreated to a quake-resistant shelter in the complex and suffered no injuries.
After the March 11th earthquake knocked out power in the region, the wave flooded the plant's diesel generators, leaving the complex without any electricity. Workers have been struggling to stem a tide of radiation since, using makeshift methods to pump cooling water into the reactors. That work continued uninterrupted after the latest quake, according to Japan's Nuclear and Industrial Safety Agency.
Japan is facing increasing alarm from its neighbours with China expressing concern at the pumping of radioactive water into the sea from a crippled nuclear plant.
China's Foreign Ministry said it would "closely" monitor Japan's actions to end the crisis at the plant, where engineers are battling to contain radiation leaks. It demanded accurate information from Tokyo.
Power blackouts and restrictions, factory shutdowns, and a sharp drop in the number of tourists have left the world's third largest economy reeling. Many economists expect it to slip into recession this year as factory output and exports suffer.
The crippled Fukushima Daiicho nuclear power plant means power shortages and supply disruptions that will leave the economy weak for some time, Japan's central bank said today.
The Cabinet Office's assessment was equally bleak. "Japan's economy is suddenly in a severe condition due to the effects of the earthquake," it said after releasing a monthly survey of hotel workers, restaurant staff and taxi drivers that showed a record fall in confidence to levels last seen during the depths of the global financial crisis.
The strong 7.1 magnitude aftershock last night - one of the biggest of more than 400 aftershocks above magnitude 5.0 - shook the already ravaged northeast. It forced two companies, including electronics giant Sony Corp , to stop production due to power cuts. At least two people were killed after the tremor.
There was a brief scare when water leaks were found on Friday at a second nuclear plant, Onagawa, in the northeast, but Japan's nuclear safety agency said it had not detected any change in radiation levels.
Agencies