David Cameron says there is severe concern about a number of British nationals missing in Japan. 

The Prime Minister says the government is sending four teams to the region affected by the quake and tsunami to try to get more information. 

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Engineers are trying to prevent a third explosion at a nuclear power plant.

There are reports the fuel rods at the Fukushima facility are now melting.

Addressing the House of Commons, the PM said Britain is ready to help.

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