Runners undeterred by thick smog engulfing the Chinese capital ran the Beijing Marathon maskless on Sunday, many wearing shorts in one of the warmest Octobers on record.
Despite a greyish brown smog settling, some 30,000 marathoners set off at 7:30 a.m. (2330 GMT) from Tiananmen Square on the route through four districts of the Chinese capital over 42.195 km (26.2 miles).
Beijing was the fourth most-polluted major city in the world on Sunday, according to Swiss air-quality technology firm IQAir.
In the Haidian district on Beijing's outskirts, the sky looked dreary, but hikers and visitors showed up at the Fragrant Hills Park where many go to enjoy autumn foliage, according to a Reuters witness.
China's national forecaster advised the public to wear masks, warning on Sunday morning that air quality was reaching moderate or severe pollution.
Smog and fog will blanket parts of China for the next few days, reducing visibility and affecting travel in northeastern, northern, central and some eastern provinces, the National Meteorological Center said on Sunday.
The smoggy weather is expected to gradually weaken and dissipate from Friday, but not before heavy fog forecast to cover parts of Jiangsu, Anhui and Sichuan provinces over the next three days could reduce visibility to less than 200 metres (650 feet), the forecaster said.
Steel production hubs in Tangshan, Handan and other cities in the northern province of Hebei launched emergency responses on Friday after heavy air pollution forecasts. The notices did not indicate when the controls would be lifted.
The smog adds unusually warm October weather, due to significantly weaker cold air currents from the north as the polar vortex that sends cold air southward was situated further north recently, experts said.
Beijing's high on Sunday was 19 C (66 F), according to the national weather bureau.
Parts of China, including in the north and northeast, have been experiencing temperatures 2 to 4 degrees Celsius (4-7 Fahrenheit) higher than normal the past 10 days.
"At present, a total of 237 national meteorological stations have broken historically highest temperatures in late October, which is still a relatively rare situation," meteorological bureau's chief forecaster Fang Chong was quoted by state media as saying.
Weak cold air currents were forecast to last the rest of the month before beginning to cool in early November.
While the smog was expected to clear up in less than a week, the backdrop of hazy weather resembled that of Beijing's annual race almost a decade ago. In 2014 then-Premier Li Keqiang, who died on Friday, declared "war" on pollution and many marathoners donned masks for protection.