BEIJING -- Beijing issued a blue alert for heavy air pollution, forecasting smog from late Monday.

The alert, effective from 3:30 pm, is forecast to last one day, according to a statement by the city's air pollution emergency response office.

A blue alert means heavy pollution with an average air quality index (AQI) of over 200 for 24 hours, according to the city's color-coded four-tier system for air pollution.

PM 2.5 is forecast to exceed 150 micrograms per cubic meter of air under the alert.

In neighboring Tianjin Municipality, a higher yellow alert was issued Monday, forecasting daily average AQI exceeding 200 for two consecutive days.

According to the municipal environmental protection bureau, it initiated an emergency response Monday, banning construction and fireworks. Emission of major pollutants must be reduced by 30 percent under the response.

Air quality will improve in the region late Tuesday when a cold front is expected.

Under China's four-tier alert system for pollution, red is the most severe, followed by orange, yellow and blue.