At least 15 people have been admitted to hospital with symptoms of radiation poisoning after a devastating earthquake damaged Japan's Fukushima nuclear power plant, Kyodo news agency said on Sunday.
A blast ripped through Number One reactor of the plant on Saturday, destroying the building, but leaving the nuclear reactor itself undamaged, according to official Japanese reports.
The blast occurred after the massive earthquake of magnitude 9 rattled the country's northeast on Friday, killing more than 1,000 people. The authorities on Sunday increased the magnitude of the quake to 9 on the the richter scale from earlier measurement of 8.9.
A steel container covering the reactor protected it from the blast, the authorities said.
Following the explosion, however, the authorities expanded the evacuation area around the plant from a 10-km radius to 20 km and began distributing iodine, which helps protect the body from radioactive exposure, to the residents of the locality.
The Fukushima prefecture authorities urged the people to close windows, turn off air conditioners and stay at home.
The emergency cooling system has failed at another reactor at the Fukushima plant, raising fears of a possible blast due to overheating, the Kyodo news agency reported on Sunday, quoting Japanese Chief Cabinet Secretary Yukio Edano.
The Number Three reactor is in process of releasing radioactive steam, Edano said.
It was the sixth reactor at the Fukushima plant to undergo cooling failure since the earthquake and tsunami hit Japan on Friday.