BEIJING, April 17 (Xinhua) -- Beijing issued a yellow alert for air pollution Tuesday.

Yellow alert means the average daily air quality index (AQI) in the city will exceed 200 for at least two days.

Beijing will see its air moderately or seriously polluted from Tuesday night. Cold air and rain on Friday are expected to improve the air quality, according to Beijing Municipal Environmental Protection Bureau.

China National Environmental Monitoring Center said that the central and southern areas of the Beijing-Tianjin-Hebei would be affected.

Response measures including dust control in construction sites, suspension of construction work and heavy vehicle restrictions will be taken from Wednesday.

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