Third blast at Japan nuclear plant
A quake-stricken nuclear plant in Japan has been hit by a third explosion in four days, amid fears of a meltdown.
The blast occurred at reactor 2 at the Fukushima Daiichi plant, which engineers had been trying to stabilise after two other reactors exploded.
The protective chamber around the radioactive core of reactor 2 has been damaged and radiation levels near the plant have risen, officials say.
The crisis was sparked by a 9.0-magnitude quake and tsunami on Friday.
Thousands of people are believed to have died, and millions are spending a fourth night without water, food, electricity or gas. More than 500,000 people have been left homeless.Staff evacuation
A fresh explosion rocked reactor 2 at the Fukushima Daiichi plant - 250km (155 miles) north-east of Tokyo - in the early hours of Tuesday.
Radiation levels around Fukushima for one hour's exposure rose to eight times the legal limit for exposure in one year, said the plant's operator, the Tokyo Electric Power Co (Tepco).
The radiation reading at 0831 local time (2331 GMT) climbed to 8,217 microsieverts an hour from 1,941 about 40 minutes earlier, Tepco said.
The annual legal limit is 1,000 microsieverts.
However, officials say that a level of one million microsieverts would be needed to cause widespread radiation sickness.
Some staff have been evacuated from the plant, but initial indications suggest it is not on the same scale as the previous blasts.
On Monday, a hydrogen blast at reactor 3 injured 11 people and destroyed the building surrounding it. That explosion was felt 40km (25 miles) away and sent a huge column of smoke into the air.
It followed a blast at reactor 1 on Saturday.
All explosions have been preceded by cooling system breakdowns. Engineers are trying to prevent meltdowns by flooding the chambers of the nuclear reactors with sea water to cool them down.
After the third explosion, officials said there were fears that the containment vessel housing the reactor may have been damaged.
Higher radiation levels were recorded on Tuesday south of Fukushima, Kyodo news agency reported.
Nearly 185,000 people have been evacuated from a 20km (12 mile) exclusion zone around the plant.Complete devastation
Meanwhile, four days after the tsunami triggered by the earthquake, the relief operation is continuing.
The latest official death toll stands at about 2,400 - but some estimates suggest 10,000 may have been killed.
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One of the worst-hit towns, Minamisanriku, is now just a scene of complete devastation, says the BBC's Rachel Harvey.
Everything was flattened by the force of the tsunami, with only the town's hospital and a government building remaining, our correspondent says.
Thousands are still unaccounted for - including hundreds of tourists - while many remote towns and villages have not been reached.
The government has deployed 100,000 troops to lead the aid effort.
They have been given 120,000 blankets, 120,000 bottles of water, tonnes of food, and 111,000 litres (29,000 gallons) of petrol to distribute.
But Hajime Sato, an official in Iwate prefecture, which also took the full force of the disaster, said it had received so far only 10% of the food and other supplies requested from the central government.
"People are surviving on little food and water. Things are simply not coming," he told the Associated Press.
The UK Foreign Office has updated its travel advice to warn against all non-essential travel to Tokyo and north-eastern Japan. British nationals and friends and relatives of those in Japan can contact the Foreign Office on +44(0) 20 7008 0000.