Two Japanese travellers have been hospitalised in China with severe radiation levels after they arrived on a flight from Tokyo.
China's customs body says they were found to have levels seriously over the limit after flying to Wuxi in the east, but were not a risk to other people.
Until now, no one in Japan except workers at a crippled nuclear power plant has been found with seriously elevated radiation levels following an earthquake and tsunami that devastated the country's north-east coast on 11 March.
The first case of contaminated Japanese travelling abroad came after injuries to workers slowed the battle to control the Fukushima Daiichi plant, Reuters reports.
Some 700 engineers have been working around the clock to stabilise the six-reactor plant since the disaster.
Engineers have been battling to cool the reactors and spent fuel ponds to avoid a large-scale release of radiation and officials now believe the No 3 reactor is more badly damaged than first thought.
Workers had to pull out of some parts of the complex when three workers replacing a cable at one reactor were exposed to high contamination by standing in radioactive water on Thursday, officials said.
Two were taken to hospital with possible radiation burns after the water seeped over their boots.
Despite increased radiation reports, fears of a catastrophic meltdown at the Fukushima plant are receding.
Two of the reactors are now regarded as safe in what is called a cold shutdown. Four remain volatile, emitting steam and smoke periodically.
Industrial catastrophe, says US expert
An American expert says the disaster at the plant is more an industrial castastrophe than a radiation crisis.
Lake Barrett, a nuclear engineer who led the initial cleanup and response at the Three Mile Island plant in Pennsylvania following a partial core nuclear meltdown in 1979, says the Fukushima plant is unlikely to be saved.
Mr Barrett says the situation should be controlled and the radioactive fallout limited sufficiently so the long-term repercussions for public health will be relatively minimal.
Toll continues to climb
The number of people confirmed dead or missing continues to climb. By Friday, 9811 people have been confirmed as dead and 17,541 people remain unaccounted for.
Authorities are burying unidentified bodies in mass graves and at least 250,000 people are still in emergency shelters, Reuters reports.
Exhausted rescuers continue to sift through the wreckage of towns and villages, retrieving bodies and pulling out photos for the consolation of survivors.
However, aid is flowing to refugees and phone, electricity, postal and bank services have begun returning to the north.