Japan expanded the evacuation zone around a crippled nuclear plant to avoid exposing residents to high levels of accumulated radiation, as the struggle to contain the worst nuclear crisis since Chernobyl entered its second month.
The operator of the wrecked Fukushima Daiichi nuclear complex said it had stopped the discharge of low-level radioactive water into the sea that had drawn complaints from neighbouring China and South Korea.
Tokyo Electric Power Company (Tepco) said 10,400 tonnes of low-level radioactive water, left by the tsunami, had been pumped back into the sea in order to free up storage capacity for highly contaminated water.
Yesterday, shortly after Japan marked one month since an earthquake and tsunami triggered the nuclear disaster, a huge aftershock shook a wide swathe of eastern Japan, killing two people, and knocking out power to 220,000 households.
The epicentre of yesterday's magnitude 6.6 tremor, which was followed by more than 25 aftershocks, was 90 miles east of the Fukushima Daiichi nuclear complex at the centre of the crisis.
The government announced earlier that because of accumulated radiation contamination, it would encourage people to leave certain areas beyond its 12 mile exclusion zone around the plant. Thousands of people could be affected by the move.
Children, pregnant women, and hospitalised patients should stay out of some areas 20 miles from the nuclear complex, chief cabinet secretary Yukio Edano told reporters.
"These new evacuation plans are meant to ensure safety against risks of living there for half a year or one year," he said. There was no need to evacuate immediately, he added.
The move comes amid international concern over radiation spreading from the six damaged reactors at Fukushima, which engineers are still struggling to bring under control after they were wrecked by the 15-metre tsunami on 11 March.
Tepco president Masataka Shimizu visited the area yesterday for the first time the disaster. He had all but vanished from public view apart from a brief apology shortly after the crisis began and has spent some of the time since in hospital."I would like to deeply apologise again for causing physical and psychological hardships to people of Fukushima prefecture and near the nuclear plant," said a grim-faced Shimizu.
Dressed in a blue work jacket, he bowed his head for a minute of silence with other Tepco officials at 2:46pm, exactly a month after the earthquake hit.
Fukushima governor Yuhei Sato refused to meet him, but the Tepco boss left a business card at the government office.
Engineers at the plant north of Tokyo said they were no closer to restoring the plant's cooling system, which is critical to bring down the temperature of overheated fuel rods and to bringing the six reactors under control.
In a desperate move to cool the highly radioactive fuel rods, Tepco has pumped water on to reactors, some of which have experienced partial meltdown.
But the strategy has hindered moves to restore the plant's internal cooling system as engineers have had to focus on how to store 60,000 tonnes of contaminated water.
Engineers are also pumping nitrogen into reactors to counter a build-up of hydrogen and prevent another explosion sending more radiation into the air, but they say the risk of such a dramatic event has lowered significantly since 11 March.
The triple disaster is the worst to hit Japan since the Second World War, leaving nearly 28,000 dead or missing.