Chinese experts have said low levels of radioactive materials detected in the air of China's northeastern Heilongjiang Province over the weekend were no threat to public health.

Su Xu, a researcher with the Chinese Center for Disease Control and Prevention (CDC), insisted the levels of the radioactive iodine -131 did not pose any health risks.

"There is no need to take special protective measures, such as keeping indoors, wearing breathing masks or taking stable iodine pills," Su said.

China started to detect low levels of radioactive iodine-131 in Heilongjiang Province on Saturday and continued to monitor the same radiation Sunday, but largely unchanged from Saturday's levels, according to China's National Nuclear Emergency Coordination Committee.

Su said authorities would continue to monitor air, water and food in northeastern China, as well as coastal regions and Beijing, and the public should be informed of the results in a timely manner.

Deng Haihua, spokesman for the Ministry of Health, said high levels of radiation had so far been detected on three people coming into the country from Japan.

"The three who have been receiving medical treatment, remained healthy and would not affect others," he said.

Deng said health authorities have designated 66 medical organizations in 31 provincial regions to test for radioactive contamination.

Li Yuanping, spokesman for the General Administration of Quality Supervision, Inspection and Quarantine, said China has banned imports of milk, vegetables, fruits and aquatic products from Japan's radiation contaminated areas to ensure food safety.

"The administration also requires local inspectors to strengthen supervision on radioactive levels of other imported food from Japan so as to prevent the contamination from entry into China," Li said.