Chinese officials on Friday called on Japan to curb the flow of thousands of tons of radioactive waste water into the Pacific Ocean from the crippled Fukushima nuclear power plant.
Japan had informed China about the event, and China "is naturally concerned" as a close neighbor, according to foreign ministry spokesman Hong Lei.
Hong urged Japan to "act in line with relative international laws and take substantial measures to protect the ocean environment," the official Xinhua news agency reported.
The agency said China was closely watching the situation, conducting monitoring, and keeping in contact with Japan.
The plant's operator Tokyo Electric Power Co. (TEPCO) released 11,500 tons of low-level radioactive water into the sea as it grappled to resume control over reactors severely damaged by the March 11 quake and tsunami.
Meanwhile, Chinese officials said they had detected "minimal" amounts of radioactive material in the skies across the country.
Trace levels of radioactive isotope cesium-137 and -134 were detected in the air of at least 24 cities and provinces, official media reported.
Xinhua said that "extremely low levels" of another radioactive isotope, iodine-131, were detected in the air over most regions.
"The radioactive materials pose no threat to public health or to the environment," China's National Nuclear Emergency Coordination Committee said in a statement on Friday, linking the radiation to the Fukushima disaster.
"No protective measures need to be taken against contamination from these materials," the statement said.
An official who answered the phone at the propaganda office of China's Ministry of Health confirmed the reports.
"Yes, but there are no new developments," the official said.
Asked about the effects on human health, the official declined to comment.
"You will have to ask an expert from one of our specialist departments," the official said. "We have already put the answers to some of these questions on our website, including whether or not the levels are harmful."
Loss of public trust?
Beijing resident Wu Tianli said the majority of ordinary Chinese people distrust what the government says, however.
"They say the levels are very low, and that they won't have an impact on human health, but I don't believe them at all," Wu said.
"They can't cover this up, or at least they won't be able to for long ... It's a terrible thing, to lose the trust of the public," she said.
In the absence of definite government advice, people are learning about possible protective measures to take by word of mouth, she said.
"Some people are saying that we should eat less fruit or leafy vegetables ... We will just have to do whatever we can to protect ourselves," Wu said.
Others were warning each other not to eat fish or seafood, because the majority of radioactive material had gone into the Pacific Ocean, she said.
Officials across China tried to dispel public fears last month following widespread panic-buying of salt, which was believed to offer protection against the uptake of radioactive iodine by the body.
Radioactive elements from Japan's nuclear crisis are making their way across Asia, prompting people and governments to take a range of precautionary measures.
Authorities across the region have already begun to test Japanese food for radiation, while some vegetables grown near Fukushima have been banned altogether.
Reported by Fang Yuan for RFA's Mandarin service. Translated and written in English by Luisetta Mudie.