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.
The upgrade came as new data today showed that more radiation leaked from its earthquake-crippled power plant in the early days of the crisis than first thought.
Japanese officials said it had taken time to measure radiation from the plant after it was smashed by lat month’s massive quake and tsunami, and the upgrade in its severity rating to the highest level on a globally recognised scale did not mean the situation had suddenly become more critical.
"The situation at the Fukushima Daiichi plant is slowly stabilising, step by step, and the emission of radioactive substances is on a declining trend," prime minister Naoto Kan told a press briefing today.
Mr Kan said he wanted to move from emergency response to long-term rebuilding.
"A month has passed. We need to take steps towards restoration and reconstruction," he said. He also called on opposition parties, whose help he needs to pass bills in a divided parliament, to take part in drafting reconstruction plans from an early stage.
The operator of the stricken facility appears to be no closer to restoring cooling systems at the reactors, critical to lowering the temperature of overheated nuclear fuel rods.
Japan's science ministry said small amounts of strontium, one of the most harmful and long-lasting radioactive elements, had been found in soil near Fukushima Daiichi.
Hidehiko Nishiyama, a deputy director-general of the Nuclear and Industrial Safety Agency (NISA), said the decision to raise the severity of the incident from level 5 to 7 - the same as the Chernobyl disaster in Ukraine in 1986 - was based on cumulative quantities of radiation released.
No radiation-linked deaths have been reported since the earthquake struck, and only 21 plant workers have been affected by minor radiation sickness, according to chief cabinet secretary Yukio Edano.
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).
The World Health Organisation said the risk to public health is no worse after a change in the disaster's status. "Our public health assessment is the same today as it was yesterday," WHO spokesman Gergory Hartl said. "At the moment there is very little public health risk outside the 30km (evacuation) zone."
He said he higher severity rating was the result of combining the amounts of radiation leaking from three reactors and counting them as a single incident.
Several experts said the new rating exaggerated the severity of the crisis.
"It's nowhere near that level. Chernobyl was terrible - it blew and they had no containment, and they were stuck," said nuclear industry specialist Murray Jennex, an associate professor at San Diego State University in California. "Their containment has been holding, the only thing that hasn't is the fuel pool that caught fire."
The blast at Chernobyl blew the roof off a reactor and sent large amounts of radiation across Europe. The accident contaminated vast areas and led to the evacuation of well over 100,000 people.
Nevertheless, the increase in the severity level heightens the risk of diplomatic tension with Japan's neighbours over radioactive fallout. Chinese premier Wen Jiabao told Mr Kan today he was "concerned" about the release of radiation into the ocean.
China has so far been sympathetic rather than angry, though it and South Korea have criticised the plant operator's decision to pump radioactive water into the sea, a process it has now stopped.
The March earthquake and tsunami killed up to 28,000 people and the estimated financial cost stands at $300 billion, making it the world's most expensive disaster.
Japan's economics minister warned the damage was likely to be worse than first thought as power shortages would cut factory output and disrupt supply chains.
Reuters