BEIJING, Nov. 3 (Xinhua) -- Beijing Friday issued an orange alert for air pollution in the coming days, advising children and the elderly to stay indoors.
The alert, the second highest level, will come into effect from Saturday, said Beijing's air pollution emergency response office.
Beijing, Tianjin, Hebei and their neighboring regions are forecast to see slight to severe air pollution from Saturday to next Wednesday, said the Ministry of Environmental Protection.
In Beijing, the air will gradually improve from Tuesday night when a cold front arrives, the ministry said.
The office advised children, the elderly and those suffering from respiratory and cardiovascular diseases to stay indoors, and kindergartens, primary and middle schools to cancel outdoor activities.
The office ordered some manufacturers to reduce production and some construction sites to halt work. Heavily polluting vehicles and trucks carrying construction waste and dirt were banned from roads.
According to the local air pollution emergency response plan, an orange alert should be issued when the average air quality index (AQI) is forecast to exceed 200 for three consecutive days and and one of those day is forecast to be over 300.
Under China's four-tier warning system, red is the most severe, followed by orange, yellow and blue.
The Beijing-Tianjin-Hebei region sits in the heart of the North China Plain where air pollution, particularly winter smog, often occurs as a result of the high concentration of industrial and vehicle emissions, limited air circulation and the burning of coal.
More residents are increasingly worried about the health impacts, particularly of PM 2.5. The smaller particles pose a greater health threat as they can get deeper into the lungs than larger particles.
China has set a target to reduce the average PM 2.5 level by at least 15 percent in the cities around the Beijing-Tianjin-Hebei region between October 2017 and March 2018, compared to last year's level.
Authorities in Tianjin and neighboring Hebei Province previously ordered heavily polluting industries, including steel, casting and coking, to restrict production and cut emissions in the winter heating period.
Authorities in the region have been also helping more households switch from coal-fired heating sources to gas and electric sources.
A total of 1.21 million households in Tianjin will switch to clean energy-fired heating sources in 2017 and 2018. In Hebei, 1.96 million households will finish the shift in 2017.