Heavy smog has hit several provinces in eastern China including Jiangsu, where Nanjing is located. There, a heavy fog red alert was issued on Monday afternoon, the most severe level of a four-tier system, and an orange warning for pollution.
Many flights out of the city's main airport were delayed on Tuesday because of poor visibility.
Major roads and bridges in the province were closed and locals were advised by police to travel by train or subway.
Jiangsu Meteorological Bureau warned people to reduce their outdoor activities and take care if using the roads.
Children and the elderly, in particular, were urged to take preventive measures to reduce the health risk from the air pollution.
The smog is predicted to end on Saturday or Sunday as cold air moves in to the region.
- South China Morning Post