The government in Japan has said radiation from the quake-stricken Fukushima nuclear plant has now reached harmful levels.
Four reactors at the plant have now exploded.
It is now thought one of the reactor’s containment systems has also been damaged, raising fears of further and more serious radiation leaks.
The UN’s weather agency said the current conditions are dispersing the radioactive particles out over the ocean, and there is no risk to people.
The World Health Organisation said by extending the exclusion zone, Japan is taking all the right precautions.
The plant’s operators, Tokyo Electric, said they have asked the US military for help.
Experts revealed that levels of up to 400 units of radiation an hour have been recorded at the site. Exposure to anything over 100 units a year is thought to be harmful.