China said it found higher than normal levels of radiation on two Japanese tourists who arrived on Friday.
The report came the same day that the government banned food imports from areas of Japan where contaminated produce and milk have been found.
A government agency said pair's radiation levels were found to "seriously exceed" levels considered safe. However, it did not provide exact numbers, making it impossible to evaluate whether the finding contradicted Japan's own assessment of the situation of a tsunami-damaged nuclear power plant.
Japanese health authorities say radiation in the air has not reached dangerous levels outside the immediate area of the Fukushima Dai-ichi nuclear complex, though some people who live near the plant have been decontaminated.
China's General Administration of Quality Supervision, Inspection and Quarantine said on its website that the two tourists were given medical treatment when they arrived in Wuxi, a city close to Shanghai, from Tokyo on Wednesday. The pair presented no radiation risk to others, it said.
It said the they were not from areas close to the nuclear power plant in northeastern Japan that has been leaking small amounts of radiation since being damaged in the March 11 earthquake and tsunami. The plant is 140 miles (220 kilometers) from Tokyo.
It gave no other details, including the pair's medical ailments.
Several countries have begun screening passengers and goods as they arrive at airports from Japan. Indonesia announced Firsay it would do so as well.
As operators of Japan's nuclear plant struggled to get its cooling system operating again, radiation has seeped into the air and water, stoking fears about the safety of Japan's food and water supply. Radiation has been found in raw milk, seawater and 11 kinds of vegetables grown in areas around the plant, and several countries have banned food imports from affected areas.
China joined them Friday, barring imports of dairy products, fruit, vegetables, and aquatic products, from five prefectures affected by radiation from the damaged nuclear plant _ Fukushima, Ibaraki, Gunma, Tochigi, and Chiba.
Stepped-up radiation testing was also ordered for all food imports from Japan.
The ban is not expected to have a major effect on trade between the two countries. Official Chinese figures show the nation last year imported $593 million worth of food products from Japan, less than 1 percent of imports from the country totaling $303.6 billion.