Fog and pollution descended on northern China on Sunday, forcing international golf and tennis players to play in hazardous smog and leading to flight cancellations and road closures as millions of Chinese headed home from an extended national holiday.

On Beijing's biggest weekend of the year for sports so far, spectators at the China Open tennis tournament and an inaugural ladies golf tournament pulled their shirts up over their faces and used masks and bandanas to try to avoid the noxious air.

"It's not ideal in terms of pollution," the world's No. 1 men's tennis player, Novak Djokovic, said after overcoming the smog and Rafael Nadal to win his fourth China Open title.

"Yes, we've been talking about the weather conditions, but it is what it is, it's something that has been the same for the last few years that I've been coming back here," the Serbian told reporters at a post-match news conference.

At the Reignwood LPGA Classic, the first Ladies Professional Golf Association event held in China, tee times were delayed to allow some of the smog to dissipate, but some players, including Germany's Sandra Gal, still donned masks.

In some areas of Beijing, visibility dropped to less than 500 meters (yards) on Saturday night and Sunday morning, according to the National Meteorological Center. It said the haze hanging over a large area of northern China, including Hebei province, which neighbors Beijing, and the port city of Tianjin would persist until Monday afternoon.

The oppressive smog in the capital sparked a high pollution alert from the U.S. Embassy, which monitors air quality. In an email to American citizens, it said its readings had averaged more than 300 on its air quality index in the 24 hours beginning Friday evening and more than 400 overnight Saturday. Anything over 301 on the U.S. Environmental Protection Agency scale is considered hazardous to health. It recommended people stay indoors and run air purifiers continuously.

The smog came during one of China's peak travel times — the Oct. 1-7 holiday known as Golden Week, when hundreds of millions of Chinese travel. The holiday is characterized anyway by long lines of traffic and delayed journeys, complicated further Sunday by the partial closure, according to state media, of six inter-provincial expressways, including one linking Beijing and Shanghai. Nearly 30 highways were also restricted around the Beijing-Tianjin-Hebei area.

Beijing Capital International Airport said four international flights were canceled Sunday morning, including to Mongolia and Russia, while three others were delayed. Two domestic flights were canceled and 20 delayed.

The airport said on its microblog at lunchtime that flights were gradually returning to normal and that visibility was more than 800 meters (half a mile) and was expected to increase further to 1,000-1,500 meters (nearly one mile) on Sunday afternoon.

___

Associated Press writer Christopher Bodeen contributed to this report.