An environmental pressure group claimed on Monday that Chinese factories are illegally using ozone-depleting CFCs, which have recently seen a spike in emissions that has baffled scientists.
The Environmental Investigation Agency (EIA) campaign group said 18 factories in 10 Chinese provinces they looked into admitted to using banned chlorofluorocarbons.
Producers and traders told EIA researchers posing as buyers that the majority of Chinese companies manufacturing foam -- in high demand as an insulator in the booming construction sector -- continue to use CFC-11 because of its better quality and lower price.
CFCs are chemicals that deplete the ozone layer, the thin gaseous shield that protects life on Earth from dangerous solar rays.
They were banned under the internationally binding 1987 Montreal Protocol and production of CFCs officially ended in developing countries in 2010.
Chinese authorities said the country successfully ended the industrial practice of using CFCs in 2007. The environment ministry in Beijing could not immediately be reached for comment.
A representative from one company cited in the report said the firm sources CFCs from unlicensed factories with "shady" operations in Inner Mongolia and conceals the substance from customs agents.
Others cited in the report said their companies produce the substance themselves, with one source saying its factories can produce 40 tonnes of CFC agents per day.
Traders cited by EIA also said that Chinese companies export the banned CFC agents by mislabelling them as Hydrofluorocarbon (HFC) compounds and other chemical blends.
Given the volume of exports of such compounds to other countries primarily in Asia and the Middle East, there is a good chance nations that have pledged to ban CFCs have inadvertently imported them, the report said.
"If China doesn't stop this illegal production, it will imperil our slowly healing ozone layer," said Alexander von Bismarck, EIA US Executive Director.
"CFC-11 is also a super global warmer, making this a serious threat for our climate as well," he added.
The report comes ahead of a working group of the Montreal Protocol in Vienna from 11-14 July, where the issue of rogue CFC-11 emissions is likely to be on the agenda.
In May, an international team of scientists published research that showed the decline of CFC-11 in the atmosphere had slowed by half since 2012, suggesting it was being secretly produced despite the global ban.
Researchers said the data pointed to East Asia as the source of renewed production but they stopped short of naming a specific country.
At present, Earth is on course for several degrees of warming by 2100, scientists say. This would doom many parts of the planet to worsening floods, droughts, desertification, rising seas and storms.