Health risks from Japan's quake-hit nuclear power reactors seem fairly low and winds are likely to carry any contamination out to the Pacific without threatening other nations, experts say.
The Japanese authorities are battling to stop fuel rods in the damaged Fukushima No. 1 nuclear power plant from overheating.
An explosion damaged a building housing a reactor on Saturday and seawater is being used to cool two reactors.
The secretary of the UN Scientific Committee on the Effects of Atomic Radiation, Malcolm Crick, told Reuters it was not a serious public health issue at the moment.
He said a partial meltdown of the Three Mile Island plant in the United States in 1979 - an accident rated more serious than Japan's present crisis - released low amounts of radiation.
The World Health Organisation (WHO) also said the public health risk from Japan's atomic plants remained "quite low".
The Japan Meteorological Agency said that the winds in the area would shift from the south to a westerly on Sunday night, blowing from Fukushima towards the Pacific Ocean.
The United States Nuclear Regulatory Commission said the US was not expected to experience "any harmful levels" of radiation.
Europe campaigners call for nuclear re-think
Tens of thousands of people have protested in Stuttgart, Germany against the government's plans to extend the life of its nuclear reactors, in a demonstration planned before the crisis in Japan.
Elsewhere in Europe, campaigners say the nuclear crisis in Japan is proof nuclear power is dangerous and governments need to rethink plans for any new plants.
Many countries planning new nuclear power plants regard nuclear as a clean alternative to expensive and dwindling oil and gas and say new technology should allay safety fears.
But the European Union policy campaigner for Greenpeace, Jan Haverkamp, says the Japanese situation is a lesson for European governments.
A British Green MP, Caroline Lucas, says human error, design failure or natural disaster can never be ruled out where nuclear power plants are concerned.