Six firefighters from West Sussex are joining the rescue mission in the aftermath of the earthquake and tsunami in Japan.

Two of the group have only just returned from New Zealand, where they were sent to help the government after an earthquake at the capital city, Christchurch.

A spokesman for West Sussex Fire and Rescue Service said: "The scale of the damage and destruction is still emerging and the Japanese government has this morning formally requested assistance from the UK to help with search and rescue operations."

The men are members of the technical rescue unit based in Horley.

St John Stanley and Mick Lewin, from Billingshurst, Chris Kemp, from Horsham, Joe Sacco and Brian Vincent, from Worthing, and Peter Thorpe-Hincks, from Steyning, are joining a 63-strong team of rescuers from the UK at Manchester Airport today.

A flight has been chartered by the Department for International Development and is due to leave between 3pm and 4pm today.

Mr Thorpe-Hincks and Mr Vincent only returned from New Zealand on Tuesday.

Sean Ruth, deputy chief fire officer for West Sussex, said: "Two overseas deployments in such a short space of time is clearly exceptional, but shows the great commitment from the whole of our team to be able to respond anywhere in the world at such short notice." The unit is one of 13 "urban search and rescue teams" in the UK, which are specially trained to work overseas with the UK International Search and Rescue Team.

They are trained to use equipment to lift, cut and remove concrete and rubble, as well as using cameras and listening devices to find survivors.

The West Sussex team is expected to run from a temporary base and organise the logistics for the rest of the UK team.

Meanwhile Japan's government spokesman said an explosion that tore through a nuclear power plant today in one of the worst-hit areas of the country did not affect the reactor.

Footage on Japanese television showed the walls of one building at the Fukushima Dai-ichi plant had crumbled, leaving only a skeletal metal frame block standing. Puffs of smoke were seen spewing out of the plant.

Yukio Edano said the metal container sheltering the nuclear reactor was not affected by the blast that destroyed the building it is in.

The radiation around the plant did not rise after the blast but instead was decreasing, said the spokesman.

Pressure and heat have been building at the nuclear reactor since an earthquake and tsunami on Friday caused its cooling system to fail.

The government has ordered people within a 12 mile radius of the plant in Fukushima to evacuate the area.

Friday's earthquake hit at 2.46pm (5.46am GMT) local time, unleashing a tsunami that reached heights of more than 20ft and crashed into the eastern coast of Japan.

The quake was followed by at least 12 powerful aftershocks,

It struck at a depth of six miles, about 80 miles off the eastern coast and about 240 miles north east of Tokyo.

Foreign Secretary William Hague said: "We are all appalled by the scenes of devastation, by the heavy loss of life, by the destruction we have all witnessed on our television screens.

"I think all over the world, people's hearts go out to the people of Japan.

"I spoke to the Japanese foreign minister today to convey our condolences, and also our offer of help."

The Foreign Secretary said the Government was "concerned" about British citizens who may have been in the affected area, particularly in north-eastern Japan.

He said: "We have no confirmed British casualties as yet, but of course the picture will become clearer as recovery teams do their work, as communications are re-established in the affected area."

The Government has sent reinforcements to the British embassy in Tokyo, he said.