China has discovered almost 30 metric tons of CFC-11, a banned ozone-depleting substance, at two illegal factories in two provinces, a senior environmental official said on Wednesday. 

About 178 tons of raw materials used to make CFC-11 were also confiscated, Liu Youbing, a spokesman for the Ministry of Ecology and Environment, told a news conference in Beijing.

People involved in the illegal production at the two factories, in the provinces of Liaoning and Henan, have been transferred to the judicial authorities for prosecution, he said, and the confiscated materials, which have been sealed up for safekeeping, will be disposed of by qualified companies. 

He said the ministry has scrutinized 1,172 companies in a special campaign targeting ozone-depleting substances launched in early August, and found CFC-11 in some batches of raw materials at 10 enterprises. They will subject to investigation and punishment by local environmental authorities, Liu said. CFC-11 has been banned in China since 2010. 

Liu reiterated the country's "zero tolerance" policy to the illegal use and production of ozone-depleting substances and vowed to enhance monitoring and supervision. 

In the past nine years, 73 cases involving the illegal use, production and sale of ozone-depleting substances have been uncovered. Fourteen of the cases were related to illegal production of CFC-11 and 84 tons of the substance have been seized and disposed of, according to the ministry. 

Since China joined the Montreal protocol in 1991, the country's reduction of ozone-depleting substances has accounted for about half the total reduction by developing countries, Liu told an earlier news conference.