Britons are being advised to consider leaving Tokyo as the crisis at Japan's stricken nuclear plant appeared to worsen.
Frantic attempts to cool down the reactors at the Fukushima Dai-ichi plant following Friday's earthquake and tsunami had to be suspended after high radiation levels were recorded.
Technicians later returned, but it was another setback in Japanese efforts to avoid a nuclear catastrophe.
The Foreign Office issued advice to any British nationals in - or to the north of - Tokyo to consider leaving the area because of the "evolving situation" in Fukushima and potential disruptions to the supply of goods, transport, communications and power.
Five days on, and as snow fell, the official death toll from the disaster reached more than 4,000, and is likely to rise substantially with more than 8,000 people missing.
A team which wanted to help in the rescue effort said it was prevented from travelling to the disaster zone because the UK embassy in Tokyo refused to issue the necessary documentation. But Foreign Secretary William Hague pinned the blame for the aborted mission on the team's own failure to be properly equipped.
In a rare address to the nation, Emperor Akihito, 77, said: "It is important that each of us shares the difficult days that lie ahead."
He added: "I pray that we will all take care of each other and overcome this tragedy."
