The European Space Agency (ESA) says extreme lockdown measures imposed by authorities in China and Italy to curb the spread of coronavirus have reduced levels of air pollution in the atmosphere.

Levels of nitrogen dioxide - released by power plants, factories and cars - plummeted across all major Chinese cities between late-January and February, according to data from the Agency's Copernicus Sentinel-5P satellite.

The drop coincided with the nationwide quarantined imposed by Beijing - as well as Lunar New Year, which ESA says usually comes with lower emissions anyway - and levels began to rise again in March as factories and schools gradually began to reopen.

Claus Zehner, the Copernicus Sentinel-5P mission manager, said he "can certainly attribute" a part of the drop to coronavirus.

"We currently see around a 40 percent reduction over Chinese cities, however these are just rough estimates, as weather also has an impact on emissions," he said.

A report by climate website Carbon Brief in February found China's industrial sector suffered a reduction in output of between 15 percent and 40 percent during the lockdown.

The ESA's timelapse of concentrations of nitrogen dioxide levels across China from late December to March.

The agency also saw a similar drop in Italy, which has surpassed China in deaths from Covid-19 and introduced a total lockdown on March 9, lasting until April 9.

All restaurants, bars, museums, schools, and other public venues are closed throughout the country, and Italians have been told to stay inside.

Mr Zehner said the lockdown was already starting to have effects on the air pollution, because of "less traffic and industrial activities."

“The decline in nitrogen dioxide emissions over the Po Valley in northern Italy is particularly evident," he said.

The ESA's timelapse of changes in nitrogen dioxide emissions in Europe and Northern Italy.

Northern Italy is the industrial heartland of the country, and many of its factories were forced closed during the lockdown.

Data tracking company TomTom found traffic congestion levels in Italian cities to have dropped significantly, with time spent in traffic dropping 64 percent in Milan, and 67 percent in Rome.

In New York, which has been under a near-total lockdown starting this week, car traffic was reduced by about 35 percent compared to the same period last year.

NASA said satellites had seen plenty of empty highways and bridges in Wuhan during the lockdown, and estimated domestic flights in the country had dropped by 60 to 70 percent, compared to the year before.

Venetians reported cleaner waters in their canals since the lockdown was put in place. Credit: PA

On social media this week, users shared images of unusually-clear waters in the Venetian canals.

The water in the canals is usually cloudy due to the high volume of motorboats and cruise ships.

But this week residents said pollution levels had dropped to the point where they could see fish, according to Reuters.

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