BEIJING, China — The coronavirus epidemic that has paralysed the Chinese economy may have a silver lining for the environment.

China's carbon emissions have dropped by least 100 million metric tonnes over the past two weeks, according to a study published on Wednesday by the Centre for Research on Energy and Clean Air (CREA) in Finland.

That is nearly six percent of global emissions during the same period last year.

The rapid spread of the novel coronavirus — which has killed over 2,000 and infected more than 74,000 people across China — has led to a drop in demand for coal and oil, resulting in the emissions slump, the study published on the British-based Carbon Brief website said.

Over the past two weeks, daily power generation at coal power plants was at a four-year low compared with the same period last year, while steel production has sunk to a five-year low, researchers found.

China is the world's biggest importer and consumer of oil, but production at refineries in Shandong province — the country's petroleum hub — fell to the lowest level since autumn 2015, the report said.

Economic activity in China usually picks up after the Lunar New Year holiday, which began on January 25.

But authorities extended the holidays this year — by a week in many parts of the country including Shanghai — in an effort to contain the epidemic by keeping people at home.

"Measures to contain coronavirus have resulted in reductions of 15 percent to 40 percent in output across key industrial sectors," the report said.

"This is likely to have wiped out a quarter or more of the country's CO2 (carbon dioxide) emissions over the past two weeks, the period when activity would normally have resumed after the Chinese New Year holiday."

But environmentalists have warned that the reduction is temporary, and that a government stimulus — if directed at ramping up production among heavy polluters — could reverse the environmental gains.

"After the coronavirus calms down, it is quite likely we will observe a round of so-called 'retaliatory pollutions' - factories maximising production to compensate for their losses during the shutdown period," said Li Shuo, a policy adviser for Greenpeace China.

"This is a tested and proven pattern."

Meanwhile, China's nitrogen dioxide emissions — a byproduct of fossil fuel combustion in vehicles and power plants — fell 36 percent in the week following the Lunar New Year holidays, compared with the same period a year earlier, according to another study by CREA that used satellite data.