Environmental authorities across China have inspected more than 1,100 companies as part of a campaign to halt the illegal production and use of ozone-depleting substances, or ODS.

Several companies were found to have materials that could contain CFC-11, a banned refrigerant, according to Liu Youbin, spokesman for the Ministry of Ecology and Environment.

All suspect materials and products were sealed and taken away for further testing, he said.

"The ministry will organize more inspections of key areas and enterprises based on the work of local environmental authorities to trace the source of illegal ODS. It will resolutely crack down on manufacture and sale of ODS," he said in Beijing on Friday.

China launched the national campaign in July after international media reports raised concerns that some companies may still be producing and using CFC-11, which the country banned in 2010.

CFC-11 damages the ozone layer, which shields the Earth from harmful ultraviolet radiation. Even though it has been banned, levels in the atmosphere are significantly higher than expected, according to research published in May by the Nature scientific journal.

Scientists concluded that new, illegal production and use of CFC-11 is occurring in East Asia. Some media then reported that Chinese companies were using the banned substance.

Since China joined the Montreal Protocol in 1991, the country's reduction of ODS has accounted for about half the total reduction by developing countries, Liu said at an earlier news conference.

"China always earnestly fulfills its obligations to international environmental conventions," he said. "It's illegal in China to produce or use substances controlled by the Montreal Protocol on Substances that Deplete the Ozone Layer. These activities have always been a key target for China's supervision and law enforcement work."