CHENGDU, Jan. 4 (NBD) -- China's national observatory on Tuesday issued an orange alert for smog in a number of northern, eastern and central regions.

In Cangzhou city in China's northern Hebei Province, authorities on December 16 issued an air pollution red alert for heavy smog, the most serious warning of China's four-tier color-coded warning system for severe weather, followed by orange, yellow and blue, and then renew the same warning for 18 consecutive days, till today. 

Meanwhile, the city, which have frequently seen severe smog since 2013, takes measure to eliminate its levels of pollutant PM2.5 – fine particulates which pose particular hazards to human health.

It has suspended productions of 1,160 enterprises and reduced productions of 139.

Scattered, small-scale burning and construction sites are also among the top priorities. The local authority has offered one-off subsidies to promote a switch over to natural gas or electricity to wean off coal. 

It costs the government 4000 yuan (about 575.32 US dollars) to subsidize a coal-to-gas switching per household, and 5000 yuan (about 719.16 US dollars) for coal-to-electricity switching per household.

A source with Cangzhou municipal government called for more financial subsidies from the central government to the switchings.

The city is required to reduce its annual average concentration of PM2.5 to 65 microgram per cubic meter this year, a 7% drop over last year.