Explosion At Japan Nuclear Power Plant

A massive explosion has rocked a Japanese nuclear power plant after Friday's devastating earthquake.

A huge pall of smoke was seen coming from the plant at Fukushima and several workers were injured.

Japanese officials fear a meltdown at one of the plant's reactors but say the container housing it was not damaged.

A huge relief operation is under way after the 8.9-magnitude earthquake and the tsunami it triggered, which is thought to have killed at least 1,000.

Japan's Prime Minister Naoto Kan declared a state of emergency at the Fukushima Daiichi and Daini (also known as Fukushima 1 and 2) power plants as engineers try to confirm whether a reactor at one of the stations has gone into meltdown.

Television pictures showed a massive blast at one of the buildings of the Fukushima-Daiichi plant, about 250km (160 miles) north-east of Tokyo.

A huge cloud of smoke billows out and large bits of debris are flung far from the building.

Japan's NHK TV showed before and after pictures of the plant. They appeared to show that the outer structure of one of four buildings at the plant had collapsed after the explosion.

The Tokyo Electric Power Co (Tepco), the plant's operator, said four workers had been injured.

It is not yet clear in exactly what part of the plant the explosion occurred or what caused it.

The government of Fukushima prefecture said radiation levels at the plant over one hour were equivalent to the annual allowable exposure.

Officials ordered the evacuation zone around the plant expanded from a 10km radius to 20km. BBC correspondent Nick Ravenscroft said police stopped him 60km from the Fukushima-Daiichi plant.

Japan's nuclear agency said on Saturday that radioactive caesium and iodine had been detected near the number one reactor of the power station.

The agency said this may indicate that containers of uranium fuel inside the reactor may have begun melting.

Nuclear reactors at four power plants in the earthquake-struck zone automatically shut down on Friday.

In several of the reactors at the two Fukushima plants the cooling systems, which should keep operating on emergency power supplies, failed.

Without cooling, the temperature in the reactor core builds, with the risk that it could melt through its container into the building housing the system.

Pressure also builds in the containers housing the reactor.

Tepco said it was pumping water into the Fukushima-Daiichi's number one reactor in a bid to cool it down.

Analysts say a meltdown would not necessarily lead to a major disaster because light-water reactors would not explode even if they overheated.

But Walt Patterson, of the London research institute Chatham House, said "this is starting to look a lot like Chernobyl".

He said it was too early to tell if the explosion's aftermath would result in the same extreme level of radioactive contamination that occurred at Chernobyl.

The explosion was most likely caused by melting fuel coming into contact with water, he told the BBC.

BBC