BBC- Explosions at a Japanese quake-stricken nuclear plant have led to radiation levels that can affect human health, a senior Japanese official has said.
Prime Minister Naoto Kan has urged those living within 30km (18 miles) of the plant to stay indoors.
Earlier, reactor 2 at the Fukushima Daiichi plant was hit by a blast - the third reactor to explode in four days - leading to fears of a meltdown.
The crisis was sparked by a 9.0-magnitude quake and tsunami on Friday. Thousands of people are believed to have died.
Exclusion zone
A fresh explosion rocked reactor 2 at the Fukushima Daiichi plant - 250km (155 miles) north-east of Tokyo - in the early hours of Tuesday. Chief Cabinet Secretary Yukio Edano said, "Now we are talking about levels that can impact human health."
He stressed that such levels were recorded at the plant and that the "further away you get from the power plant or reactor, the value should go down".
In his televised address, Prime Minister Kan said: "There is still a very high risk of more radiation coming 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.
Higher radiation levels were recorded on Tuesday south of Fukushima, Kyodo news agency reported.