Like many other countries in the region, China is beginning to detect small amounts of radioactive materials in its atmosphere which are spreading out from Japan, sparking fear and mistrust of government claims that the levels are harmless.
China's National Nuclear Emergency Coordination Committee said on Wednesday that "extremely low levels" of radioactive iodine had been detected in the air around more Chinese areas, including Shanghai and Tianjin.
The committee said the materials posed no threat to public health.
The radioactive isotope iodine-131 was detected on Wednesday in 18 provinces, municipalities, and autonomous regions, said the statement.
"The material is believed to have drifted to China by air from the quake-damaged Fukushima Daiichi Nuclear Power Plant in Japan," it said.
Researchers from a group of atomic energy, meteorological, and environmental government agencies had concluded that no protective measures needed to be taken against contamination, the official Xinhua news agency reported.
But the Chinese public isn't so sure, according to netizens and commentators.
"The Japanese radiation situation looks like it's getting more complicated," wrote user Tangsheng Dongyou on the popular microblogging site Sina Weibo.
"It's not like the Chinese experts said it would be ... now the radiation has spread across the world on the wind, and ... the Chinese experts have all changed their tune."
User Su Xiaomeng said no one should be worried about the radiation from Japan.
"What's a bit of radioactive iodine? That's so lame," Su wrote, satirically. "We have had melamine milk, poisoned rice, dishes fried in waste oil, phosphates, Sudan Red and lean meat powder ... We've got the whole periodic table in our bodies."
"This is so that the Chinese people will survive any biological warfare."
Shenzhen-based political activist Zhu Jianguo said there is scant public trust in government statements on public health and safety among most Chinese people.
"We have already seen that the government's approach is first to denounce everything as rumor-mongering, then to say that no protective measures are necessary when they can't deny it any longer," he said.
"Even when it does admit that there is [contamination], it still takes the attitude of dispelling rumors, not one of concern about people's safety," he said.
"For this reason, everything the government says has become suspect."
Zhu said the accidents at the Japanese power plants have led to a public backlash against nuclear power in China.
"A lot of ordinary Chinese are now thinking that it would be best not to have nuclear power at all," he said.
"They think that the best prevention would be to learn a lesson from Japan, and close down the nuclear plants like Daya Bay that are in an earthquake zone."
Delay in reporting
Officials across China moved to dispel public fears last week following widespread panic-buying of salt, which was believed to offer protection against the uptake of radioactive iodine by the body.
The Hong Kong Observatory was harshly criticized by legislator James To on Tuesday after it published details of small levels of radioiodine contamination three days late.
To highlighted concerns that the observatory wouldn't inform the public in the event of a leak of radioactive material from the nearby Daya Bay nuclear power plant.
Tan Zhiqiang, assistant professor of physics at the Macau University of Technology, said the delay was probably caused by a lack of qualified personnel and equipment.
"I don't believe that the Hong Kong government has the capability to test for these things," he said. "They would have to spend a bit more money on senior personnel and equipment to do that."
"Hong Kong has no nuclear power plants, so the government hasn't invested in such things," Tan said.
Hong Kong Observatory director Lee Boon-ying said the delay in reporting radiation levels had been due to a need for accuracy.
"If you see something that you haven't seen before, you want to wipe your glasses clean and take another look, or several looks," Lee said.
"We took the decision at the time to repeat our measurements one more time, which we did on Monday, and so we didn't confirm the results until Tuesday, when we reported them to the public immediately," Lee added.
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.
As well as mainland China, South Korea, the Philippines, and Vietnam have reported some radiation drift in their atmospheres.
China has begun screening passengers arriving from Japan for elevated radiation levels, sending two Japanese travelers to hospital last week, although they were later discharged.
Taiwanese authorities have found small amounts of radioactive particles on 43 passengers from Japan since the crisis began.
Meanwhile, South Korean officials have begun testing fish caught in their own fishing grounds for caesium, iodine, and other radioactive materials.
A nuclear expert for Greenpeace International has said that the levels of radiation that were reaching countries far away are so low that they would not pose a significant health risk, although they could boost cancer rates in a very large population.
Reported by Fang Yuan for RFA's Mandarin service, and by Dai Weisen for the Cantonese service. Translated and written in English by Luisetta Mudie.