A state of emergency has been declared at a second quake-hit nuclear plant in Japan amid warnings of another explosion at the first plant.
The International Atomic Energy Agency declared the measure after excessive radiation levels were recorded at Onagawa, in the country's northern Miyagi region.
Experts at the agency said it was the lowest grade state of emergency on the scale.
They said there was no problem with the cooling process and claimed the rise was linked to another plant in a neighbouring state.
It comes after chief cabinet minister Yukio Edano warned of a hydrogen blast in reactor three at the Daiichi plant in Fukushima.
He insisted reactor three at Daiichi could withstand a potential explosion, as reactor one did on Saturday.
The first blast destroyed the building housing reactor one, but did not prompt a major radiation leak.
Mr Edano said it was highly likely a partial meltdown had occurred in one reactor of the Fukushima plant, and that authorities were working on the assumption that one may occur in another.
Operators are now attempting to reduce the risk of meltdown at a total of three of the affected reactors at Daiichi by injecting sea water into them.
Tokyo Electric Power Company (TEPCO) said it was preparing to release some steam to relieve pressure in the reactor at the plant - 150 miles (241km) north of Tokyo.
We can stabilise the reactor if we take the air out and pump water in the vessel properly," Mr Edano said.
"At the risk of raising further public concern, we cannot rule out the possibility of an explosion.
"If there is an explosion, however, there would be no significant impact on human health."
The government has insisted radiation levels are low following Saturday's explosion, saying the blast had not affected the reactor's core container.
Some 22 people have showed signs of possible exposure to radiation at the Fukushima plant.
Nuclear consultant John Large told Sky News: "They have clearly had a meltdown in reactor one, they've lost the containment there.
"They've flooded that with sea water, not necessarily to cool the fuel, but to swamp the fuel, to stop radioactive particles and aerosols actually releasing into the atmosphere.
"Reactor three is essentially fuelled with plutonium instead of uranium and plutonium has a much more significant radiological footprint.
"So it's absolutely essential that they minimise, or completely abate the radioactive release from number three if it should
Officials from the Japan Nuclear and Industrial Safety Agency say up to 160 may have suffered radiation exposure.
A 12-mile (19km) radius has been imposed on the Fukushima Daiichi plant with an estimated 170,000 people already having been evacuated.
Sky News' Holly Williams, in Fukushima, said: "The experts I'm speaking to say that at the moment, as long as people are evacuated from the area, there is very little risk to humans.
"But they say the big risk here is fire. If either of these reactors caught fire, that would spread that radiation over a much larger area, which is obviously the concern of Japanese authorities at this moment."
A six-mile exclusion zone is also in place around the nearby Fukushima Daini station, with an estimated 30,000 people told to leave the area.