BEIJING - China's capital Beijing has issued a yellow alert for smog, with more to follow over the weekend, Xinhua news agency quoted the National Meteorological Centre (NMC) as saying.

On Saturday (Oct 15) morning, Beijing's Air Quality Index (AQI) went up to 213, Xinhua cited data from the municipal environmental monitoring centre as showing.

PM2.5 fine particulate matter PM2.5 was the major pollutant, it said.

Yellow is the third-highest alert in a four-tier system.

The NMC also forecast moderate smog over Beijing and north-east Hebei Province from up to Sunday morning.

Residents in China's northern and north-eastern regions awoke to severe smog on Friday (Oct 14), prompting Beijing to raise its health alert to yellow, while some expressways closed due to limited visibility, according to the China Daily.

Beijing's AQI hit 300 on Friday afternoon, reported Xinhua.

Visibility dropped to below 200m in some areas, including the capital and the southern region of Liaoning province on Friday morning due to pollution mixed with heavy fog, leaving some expressway sections closed for hours, reported the China Daily.

On Thursday afternoon, Beijing issued a blue alert for air pollution, the lowest emergency response on a four-tier system, amid lingering smog that had covered the capital since Wednesday.

Since September, residents have seen several days with heavy smog.

The yellow alert was also triggered on Oct 2.

Major air pollutant readings soared in September, according to data from the Ministry of Environmental Protection on Thursday.