Thick smog, worsened by coal-burning, disrupted traffic and flights in northern China, state media reported today.

In the capital city of Harbin in Heilongjiang province, the local meteorological bureau issued a 'yellow alert' indicating heavy pollution over three days, the third-highest of its four-tiered alert system, late yesterday, China's state broadcaster CCTV said.

Many vehicles were stuck on the highway as they were closed due to low visibility, CCTV added.

At Taiping International Airport, 20 flights were cancelled and 38 others delayed as of 10.30am this morning due to the smog, affecting more than 4,000 passengers, CCTV reported.

In Zibo, a city in eastern Shangdong province, heavy fog reduced visibility to less than 500 metres, and in some areas, less than 100 metres.

Air pollution, mostly caused by coal-burning during the colder season, is expected to continue over the next few days, China's state run Xinhua news agency reported.

Facing mounting public pressure, leaders in Beijing have declared a war on pollution, vowing to abandon a decades-old growth-at-all-costs economic model that has spoiled much of China's water, skies and soil.