Residents of Beijing and other parts of northern China endured a third consecutive day of serious air pollution that forced the closure of highways due to poor visibility.

China’s National Meteorological Center issued a ‘yellow alert’ for haze in Beijing and its neighboring provinces on Monday morning, indicating a serious level of air pollution.

The smog prompted authorities to close highways connecting the Chinese capital to the cities of Tianjin and Shanghai, while other highway closures were ordered in Hebei province, neighboring Beijing. Vehicle traffic in Beijing’s urban areas was not affected.

Air pollution levels in Beijing soared to the highest level of six on Saturday and Sunday, coinciding with the final days of a week-long national holiday in which hundreds of millions of Chinese travel.

Chinese state media said the smog forced many vacationers to postpone their return home. Dozens of flights were delayed, diverted or canceled at Beijing’s international airport on Sunday.

An, a Beijing resident, told VOA that the haze has obscured the landscape surrounding the city.

“I live in Beijing’s West Mountain area and have a good view of the mountain. But, when the smog comes in, you see nothing. The mountain is hiding behind the smog,” said An.

Another resident, Ouyang, complained of the physical effects of the pollution.

“When you get home from the outside, you find that your nose turns black from inhaling the dust, which is harmful to one’s health. Both my nose and throat were feeling uncomfortable very much,” said Ouyang.

The smog also overshadowed the finals of international golf and tennis tournaments held in Beijing on Sunday, creating unpleasant conditions for players and spectators.

The air pollution did ease by Monday evening. The U.S. embassy in Beijing reporting of 167 at its air quality monitoring station, indicating “unhealthy” conditions, compared to “hazardous” readings of more than 300 in the previous two days.