Radiation levels rise four-fold at stricken Japan reactor

Radiation levels in the air surrounding Japan's quake-stricken nuclear power plant have risen four-fold after a fresh explosion at the site on Tuesday, the plant operator said.

The radiation reading at 8.31am local time (2331 GMT) climbed to 8,217 microsieverts an hour from 1,941 about 40 minutes earlier, Tokyo Eletcric Power Co said.

Authorities at the Fukushima Daiichi complex, damaged in Friday's massive earthquake and tsunami, are trying to prevent meltdowns in three of the plant's nuclear reactors.

Japanese authorities say levels would need to reach one million or so before causing large-scale radiation sickness.