Japan has raised the severity of its nuclear crisis to the highest level, putting it on a par with the world's worst nuclear disaster at Chernobyl in 1986 because of the amount of radiation released into the air and sea.
As another major aftershock rattled the earthquake-ravaged east of the country, a fire broke out at the Fukushima Daiichi power plant, although engineers later appeared to have extinguished the blaze.
Developments in recent days suggest the operator of the stricken facility is no closer to restoring cooling systems at the reactors, which is critical to bringing down the temperature of overheated nuclear fuel rods.
An official at Japan's Nuclear and Industrial Safety Agency (NISA) said that based on cumulative levels of radiation released, the severity of the incident had been raised to 7, the worst on an internationally recognised scale.
A senior official in Prime Minister Naoto Kan's office said the reason for raising the level to 7 a month after the disaster was that it had taken time to measure and estimate the overall radiation emitted from the damaged nuclear plant.
"Even before this, we had considered this a very serious incident so in that sense, there will be no big change in the way we deal with it just because it has been designated level 7," said the official.
It had previously been put at a 5 rating, on a par with the 1979 Three Mile Island incident in the United States.
A level 7 incident means a major release of radiation with a widespread health and environmental impact, while a 5 level is a limited release of radioactive material, with several deaths, according to the International Atomic Energy Agency (IAEA).
But some experts said the new rating exaggerated the severity of the crisis, adding the incident did not compare to the Chernobyl disaster in Ukraine a quarter of a century ago which spewed radiation over most of Europe.
City A.M. Reporter