More than 300,000 people living in the area have been told they can leave their homes but there is still a 350-metre "exclusion zone" around the plant.

However, fears persist over the effects of fallout from the accident. Officials told residents caught out in Thursday evening rain showers to wash their clothing and said locally grown vegetables should not be eaten.

The BBC's Margaret Gilmore:"People are still frightened"

Radiation levels soared to 15,000 times the normal level just after the accident - schools were shut, train services halted and farmers were warned not to harvest their crops until safety checks had been carried out.

But officials say radiation levels outside the plant have now returned to normal, and local residents are no longer at serious risk.

The BBC's Pallab Ghosh: "It will take many years for the long term health effects of the explosion to become clear"

They issued the statement after operators drained coolant water and carried out a number of other measures to reduce the risk of contamination resulting from a leak inside the uranium processing plant.

The Governor of Ibaraki Prefecture, Masaru Hashimoto, said he had received confirmation at 0615 (2115GMT) that the nuclear chain reaction at the uranium processing plant had stopped.

The aftermath of the accident coincided with the arrival on Friday of a second British ship carrying a cargo of plutonium for Japan's nuclear power industry.

The Pacific Pintail docked in Takahama, 400km (248 miles) southwest of Tokyo.

More than 30 workers at the Tokaimura plant are thought to have been exposed to radiation. Two are in a critical condition and are expected to be given bone marrow transplants.

The BBC's David Shukman: "The fear runs very deep here"

The victims include builders who had been working at the plant, people who live nearby and firemen who helped in the rescue.

Human error

Officials said workers had caused the accident at the plant by pouring too much uranium solution into a tank.

Japanese Foreign Ministry spokesperson Sadaaki Numata: "Lessons will be learnt"

Japanese Prime Minister Keizo Obuchi criticised the response to the accident, saying it had taken too long for experts to assess the seriousness of the situation.

He also held an emergency meeting of the cabinet which set up a special task force - the first time it has taken such a measure after a nuclear accident.

Washington has meanwhile announced that a joint American and Russian team is being sent to Japan.

Criticality

Chief Cabinet Secretary Hiromu Nonaka said it was very likely there had been a "criticality incident" at the plant.

Criticality is the point at which a nuclear chain reaction becomes self-sustaining.

The French nuclear institute said the incident was the 60th in the world since 1945, following 33 such accidents in the United States and 19 in the former Soviet Union.

One of the workers reportedly told an official that he had used about 16kg of uranium - nearly eight times the normal amount - during the process just before the accident.

Workers normally use up to 2.3kg of uranium in each procedure to prevent a criticality accident, officials said.

Although no official government reading has been released, local authority officials said radiation levels were about 10 times normal, 2km (1.2 miles) from the scene.

US help

US President Bill Clinton pledged US assistance to Japan in the wake of the accident.

Plant manager Makoto Ujihara briefed the press about the accident

"We are all very concerned and our thoughts and prayers are with the people of Japan today," he said.

The International Atomic Energy Agency (IAEA) described the incident as "extremely serious", and said it would send officials to the plant.

The environmental organisation Greenpeace criticised the accident as a symptom of a safety "crisis" in Japan's nuclear industry.

The leak is the latest in a series of accidents at Japanese nuclear facilities, including a previous one at Tokaimura in which 35 workers were exposed to radiation.

Japan has 51 commercial nuclear power reactors, providing one third of the country's electricity.

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