Britons affected by the Japanese disaster will be flown home to the UK free of charge on charter planes from Tokyo, the Government has announced.
Flights from the capital to Hong Kong will be laid on to help those who wish to leave the stricken country, and passengers will be able to travel back to Britain from there, the Foreign Office (FCO) said.
The offer of help came hours after Britons were advised to consider leaving Tokyo amid desperate attempts by the Japanese to prevent meltdown at the Fukushima Dai-ichi nuclear plant. The plant has been rocked by a series of explosions and fires since Friday's 9.0-magnitude earthquake and tsunami.
Updating its travel advice, the FCO said: "We continue to advise against all non-essential travel to Tokyo and north-eastern Japan and that British nationals currently in Tokyo and to the north of Tokyo should consider leaving the area.
"The UK government is chartering flights from Tokyo to Hong Kong to supplement commercially available options for those wishing to leave Japan."
The first option for leaving Japan should remain commercial routes, which continue to operate to and from Japan, they added.
Military helicopters have sprayed seawater on to damaged reactors at Fukushima Dai-ichi as they battled to bring the emergency under control. The efforts to cool reactors came as US officials warned of a shortage of water in a storage pool meant to stop nuclear fuel rods from overheating.
Earlier the FCO urged Britons to remain outside an 80km (50 mile) radius of the plant "as an additional precautionary measure". It said the call was in line with the US government's advice to its citizens in Japan.
The Royal Society of Chemistry in Cambridge cautioned against "scaremongering" over the effects of the explosions at Fukushima, as pharmacies in the United States reported a surge in people buying potassium iodide tablets, which can prevent the body absorbing radioactive iodine.
UK pharmacists said they were receiving inquiries from members of the public wishing to either stockpile the tablets at home or send them to loved ones in Japan.
