Low levels of radioactive material iodine-131 were detected Saturday in Heilongjiang Province, north of Beijing, China's National Nuclear Emergency Coordination Committee said.
The radioactive material was likely to have come from the tsunami-damaged Fukushima nuclear plant in Japan, the agency said.
However, since the radiation level was below one-hundred-thousandth of the average natural background radiation, it did not pose a risk to public health or the environment, and no protective measures were required, the agency said in a statement.
Repair work at the troubled Fukushima nuclear plant has continued into a third week. More countries are beginning to detect tiny amounts of radioactive iodine and cesium in the air that have drifted across oceans from the overheated nuclear reactors in Fukushima, where a tsunami following a 9.0-magnitude earthquake knocked out its crucial cooling system on March 11.
The Austrian capital of Vienna detected very low concentrations of radioactive particles Friday, believed to have come from Fukushima, the Austrian Agency for Health and Food Safety (AGES) said.
The detected radioactive materials were iodine-131 and cesium-137, and the tiny amount would pose no threat to human health, the Austrian agency said.
It was the first time the two radioactive materials were detected in the country since the quake struck Japan.
Sea water samples taken from about 330 meters south of the Fukushima Daiichi nuclear plant on Japan's east coast showed radioactive iodine 1,250.8 times above legal limit near the drain outlets of the reactors, local media reported Saturday.
The reading was taken on Friday morning, recording the highest radiation level so far from the surveys begun this week, plant owner Tokyo Electric Power Co (TEPCO) said.
However, radioactive materials would "significantly dilute" by the time they were consumed by marine species, Kyodo News reported, citing the agency.
The agency said the radiation would not have a significant impact on fishery products because fishing was not conducted within 20 km of the plant.
Government spokesman Yukio Edano said Saturday the situation at the stricken plant remained unpredicable, and it would be "a long time" until the crisis was over.
"To prevent situations going worse, we're trying to restore electrical supply at the plant and inject freshwater into the nuclear units to make essential improvements," Edano said Saturday. "We have to remain alert."
Japan switched to using fresh water to cool the reactors Friday, fearing salt accumulation would hurt waterflow and cooling effects. Tokyo Electric plans to launch fresh water injection at the spent fuel rods pool on Sunday, and it has injected fresh water into the No. 1, 2 and 3 reactors so far, national broadcaster NHK reported.
"The situation inside the reactor cores is not very stable and we can't say specifically how long that's going to last," Sakae Muto, executive vice president of Tokyo Electric, said late Saturday.
Koyama Kota, deputy chief of TEPCO Fukushima office, told Xinhua the nuclear accident at Fukushima Daiichi plant was very complicated. It was difficult to determine when the clean-up would be completed, he said, since the major task at present for the company was to control radiation leakage.
Meanwhile, UN Secretary-General Ban Ki-moon called Friday for international organizations and individual states to review and strengthen their nuclear safety plans.
"The existing institutional arrangement, including the Joint Radiation Emergency Management Plan of the International Organizations, with the IAEA (International Atomic Energy Agency) as the main coordinating body, needs to be reviewed and strengthened," Ban said in a statement.
According to Japan's National Police Agency, the catastrophic earthquake and ensuing tsunami had left more than 10,400 people dead and 17,000 others unaccounted for by 19:00 p.m. local time on Saturday (1000 GMT).