VIENNA (Reuters) - The U.N. nuclear watchdog said it is aware of media reports of an explosion on Saturday at Japan's Fukushima No.1 nuclear power plant and is urgently seeking information from the country's authorities.
An official at the International Atomic Energy Agency (IAEA), the Vienna-based U.N. atom body, gave no further details.
Jiji news agency said there had been an explosion at the stricken 40-year-old Daichi 1 reactor and TV footage showed vapor rising from the plant, which lies 240 km (150 miles) north of Tokyo.
Japanese media said an explosion blew the roof off the reactor, raising fears of a disastrous meltdown at a nuclear plant damaged in the massive earthquake that hit Japan.
"We are aware of the media reports and we are urgently seeking further information," the IAEA official told Reuters.
The blast came as plant operator Tokyo Electric Power Co (Tepco) worked desperately to reduce pressures in the core of the reactor that, if not contained, could lead to a release of radiation into the atmosphere.
Nuclear expert Mark Hibbs of the Carnegie Endowment for International Peace said an explosion would be a "physical shock" to the plant that could increase the danger of a breach of the containment and of radioactivity getting out.
"We don't have any information from inside the plant. That is the problem in this case," he said.
"If it melts down the probability that there would be a breach or that radiation would get outside of the plant because of weakness of the structure of the plant ... is much greater," Hibbs said.
(Reporting by Fredrik Dahl; Editing by Louise Ireland)