Trace levels of radioactive isotope cesium-137 and -134 were detected in the air of at least 22 of the Chinese mainland's 31 provincial-level regions on Thursday, according to China's National Nuclear Emergency Coordination Committee.

Cesium-137 and -134 were detected in Beijing, Shanghai, Tianjin, Chongqing, Hebei, Shanxi, Liaoning, Jilin, Heilongjiang, Jiangsu, Zhejiang, Anhui, Fujian, Jiangxi, Shandong, Henan, Hubei, Hunan, Guangdong, Shannxi, Ningxia and Xinjiang on Thursday.

The radioactive isotope Cesium-137 and -134 was found in 21 provincial-level regions on the Chinese mainland on Wednesday.

"Extremely low levels" of radioactive iodine-131 were detected in the air over some areas of all provincial-level regions except Guizhou.

The levels of cesium-137 and -134 were even lower than those of iodine-131.

They pose no threat to public health or to the environment, according to a daily statement issued by China's National Nuclear Emergency Coordination Committee Thursday.

Food and drinking water have been tested for contamination and found to be safe, according to the statement.

The materials are believed to have traveled by air to China from the quake-damaged Fukushima Daiichi Nuclear Power Plant in Japan.

No protective measures need to be taken against contamination from these materials, said the statement.

The committee's conclusion was based on monitoring and analysis results from the Beijing-based Regional Specialized Meteorological Center affiliated with the World Meteorological Organization and the International Atomic Energy Agency, the State Oceanic Administration, the Ministry of Environmental Protection and the Ministry of Health, according to the statement.

Low levels of iodine-131 were first detected in northeastern China's Heilongjiang Province on March 26.