Satellite images issued by NASA have shown a dramatic decline in pollution levels across China, which is "at least partly" due to an economic slowdown following the outbreak of the new coronavirus, the space agency said on Sunday.

NASA and the European Space Agency (ESA) pollution monitoring satellites reportedly detected significant decreases in nitrogen dioxide (NO2) over China.

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The images show concentrations of nitrogen dioxide, "a noxious gas emitted by motor vehicles, power plants and industrial facilities," according to NASA.

The reduction in NO2 pollution was first apparent near Wuhan, the city at the center of the COVID-19 outbreak in China, according to NASA scientists, but eventually spread across the country.

Millions of Chinese citizens have been quarantined, and cities placed in lockdown since the start of the novel coronavirus outbreak.

"This is the first time I have seen such a dramatic drop-off over such a wide area for a specific event," Fei Liu, an air quality researcher at NASA's Goddard Space Flight Center, said in a press release. He added that he had seen a drop in pollution levels in several countries during the 2008 economic recession, but the decrease had been gradual.

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Similar effects were also observed around Beijing during the 2008 Olympics, but they were mostly seen around the city.

China's Lunar New Year celebrations in February have also been linked to similar decreases in pollution levels. Businesses and factories typically close ahead of the festival, causing temporary reductions in pollution output.

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"This year, the reduction rate is more significant than in past years and it has lasted longer," Liu said.

China has recorded nearly 85,000 cases of coronavirus since the outbreak began in December. Quarantines and lockdowns in a number of Chinese cities have trapped hundreds of millions indoors, while more than 2,900 people have died from COVID-19 worldwide.

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lc/jlw (dpa)