China's environment ministry on Thursday warned northern regions to get ready for emergency action to tackle another bout of heavy smog expected over the New Year.

Large parts of the north were hit by hazardous smog in mid-December, and authorities ordered hundreds of factories to close and restricted motorists to cut emissions.

"Unfavourable weather" was expected to bring more smog to the Beijing-Tianjin-Hebei region, as well as the neighbouring provinces of Shandong and Henan, the Ministry of Environmental Protection said in a notice.

Beijing has raised an orange alert for the period from Friday to Monday. An orange alert is the second-highest level in a four-tier pollution warning system.

The ministry said the bad weather was expected to last until Jan. 5, and it had asked local governments to take appropriate action to reduce emissions.

It said it would send out 10 inspection teams to make sure emergency measures are implemented and to take action against firms engaging in "illegal behaviour".

Public anger over pollution, and what many see as government talk but little action to stop it, is mounting in China. Worry about pollution has on occasion sparked protests.

A smog red alert in Beijing was cancelled on Dec. 22. The next day, the ministry admonished more than 20 firms for failing to comply with emergency rules aimed at cutting emissions.

Hebei, regarded as China's most polluted province, said it would learn lessons from last week's smog and draw up more "focused measures".

The province's environment bureau said on Monday it would make adjustments to its emergency system to improve its performance.

In recent smog outbreaks, individuals and companies had not been given enough time to respond to pollution alerts, and warnings would now be issued sooner, said Wang Xiaoli, director of the province's Heavy Pollution Early Warning Centre.