The capital’s pollution levels were comparable to those in Kolkata and Delhi in India, Tashkent in Uzbekistan and Baghdad in Iraq.

Poor air quality persisted into the afternoon. Readings from the Northern Environmental Monitoring Centre showed several stations still reporting unhealthy levels, including 170 on Giai Phong Street and 155 at 556 Nguyen Van Cu.

Officials warned that dangerous air conditions may continue in the coming days.

According to the Department of Environment, major pollution sources include industrial emissions, which account for about 30 per cent; vehicle exhaust at 12-15 per cent; transport activity at 20-30 per cent; and the open burning of agricultural waste, household rubbish and construction debris.