The World Health Organization said Tuesday it was ready to help Japan, which is grappling with a nuclear emergency after some reactors were damaged by last week's deadly earthquake.
"We have expressed our availability to participate in a mission, to offer necessary assistance, if it is required," said Maria Neira, the UN health agency's director of public health and environment.
"We are ready," she added.
Radiation near a quake-hit nuclear plant reached levels harmful to human health, Japan's government said after two explosions and a fire at the crippled facility Tuesday.
Four of the six reactors at the Fukushima No.1 plant, 250 kilometres (155 miles) northeast of Tokyo, have now overheated and sparked explosions since Friday's massive earthquake and tsunami knocked out cooling systems.
The WHO assessed that Japanese authorities have acted appropriately in imposing exclusion zones around the plant.
"The actions proposed by the government of Japan are in line with the existing reommendations based on public health expertise," said the UN health agency.
However, Neira warned: "The situation is evolving very quickly, the recommendations will have to be adapted with the situation as it evolves.
"For the time being, with the core information that is available with the prevailing situation, the type of radioactivity that is in the area, the measures of evacuating, the measures of requesting people to stay indoors, the measures to preposition and eventually distribute potassium iodide, those are the ones that the public health community is recommending," she said.
Neira also said that the WHO was not making any specific recommendation on diet at the moment, as "the produce that will be at risk will be the produce that are growing in the contaminated areas."
"Our understanding is that there are no problems at the moment (from what) they've collected from the area, because it's totally innundated."