Chinese authorities have shut down scores of factories and ordered a mandatory holiday for workers ahead of a summit of leaders of the Group of 20 economic powers, authorities said.

The Hangzhou city government ordered a holiday for businesses in the downtown area from September 1 to 7, according to an official social media account. The G20 meeting will be held on September 4 and 5.

City officials have also encouraged citizens to take their holiday out of town, in the hopes of reducing congestion. The city has already spent months preparing for the meeting and has undergone a major overhaul in an attempt to make traffic more efficient.

Along with the mandatory vacation, certain types of factories within a 300-kilometre (185 mile) radius of Hangzhou have been forced to shut down for 12 days in order to ensure blue skies for the visiting dignitaries, according to government websites.

The order affects chemical producers, construction material factories and textile manufacturers stretching across Shanghai and four provinces.

China often orders mass factory closures to clean up the chronically polluted skies of most major cities. The phenomenon was apparent at a major military parade last year to mark the end of World War II.

The clear atmosphere was dubbed "parade blue" by Chinese citizens, echoing the "APEC blue" they enjoyed ahead of 2014's Asia-Pacific Economic Co-operation summit in Beijing.

At the time online commentators dismissed the hue as "something that is beautiful but fleeting and ultimately inauthentic".