BEIJING -?China's national observatory renewed a yellow alert, the third-highest level of warning, for smog on Monday morning.

Moderate smog will fall over Beijing as well as parts of north China's Hebei Province and northwest China's Shaanxi Province from Monday morning to Tuesday morning, with some areas to see heavy smog, the National Meteorological Center (NMC) said.

The smog will start to disperse gradually from Monday night, the NMC forecast.

It advised the public to take precautions, and patients with respiratory diseases were told to reduce outdoor activities.

China has a four-tier color-coded system for severe weather, with red being the most serious, followed by orange, yellow and blue.