Radiation levels near a quake-hit nuclear plant are now harmful to human health, Japan's government said after three explosions and a fire at the crippled facility. The crisis at the Fukushima No.1 plant, 250km northeast of Tokyo, has now spread to four out of its six reactors following Friday's earthquake and tsunami which knocked out cooling systems.
Tens of thousands have already been evacuated from a zone within a radius of 20km from the ageing plant, but Prime Minister Naoto Kan urged people living within 10km of the exclusion zone to stay indoors.
Edano said radiation levels as of 10:22 (01:22 GMT) on Tuesday were 30 millisieverts between the number-two and the number-three reactors, 400 millisieverts near number-three and 100 millisieverts near number-four. A single dose of 1 000 millisieverts - or one sievert - causes temporary radiation sickness such as nausea and vomiting. A dose of 5 000 millisieverts would kill about half those receiving it within a month.
Edano said radioactive substances might spread outside the 20-30km area but would dissipate the farther they spread.
It was still unclear whether the container sealing the number-two reactor had been breached.
What kind of danger will Japan face if the radiation cannot be contained?
Immediate ARS symptoms include nausea, diarrhoea and fatigue. This may be followed by symptoms such as hair loss, bleeding under the skin and mouth inflammation.
5km radius of the source: people in this area would be at highest risk for radiation exposure.
16km radius of the source: people could potentially be harmed by direct radiation exposure.
80km radius of the source: radioactive materials may contaminate water supplies, crops and livestock