Third blast at Japan nuclear plant
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.
Prime Minister Naoto Kan said the level of radiation at the plant had "considerably risen" and there was a high risk of radioactive material leaking out.
He added that the last remaining people within a 20km (12 mile) exclusion zone around the plant had to leave, and that those living between 20km and 30km from the site should remain indoors.
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; Kazinform cites BBC News.
See www.bbc.co.uk for full version
