AIR pollution in the city last night soared to nearly 15 times the World Health Organization safe level.
Levels of main pollutant PM2.5, tiny particles that can get deep inside the respiratory system, reached 360 micrograms per cubic meter at 8pm.
The WHO safe limit is 25 micrograms per cubic meter.
The Shanghai Meteorological Bureau issued a yellow haze alert at 5:20pm yesterday — a medium-level warning.
Visibility was set to fall below 500 meters through to morning, with northern and coastal areas worst affected.
Air quality was reported good yesterday morning — between 50 and 100 on the city Air Quality Index, said the Shanghai Environmental Monitoring Center. However, it worsened as the day progressed.
Pollutants are carried south from north China in winter and still conditions yesterday saw them hang over the city, Wu Rui, chief service officer at the bureau, told Shanghai Daily.
Even the arrival of rain in the afternoon failed to damp down levels.
By 8pm, the AQI hit 407 — well above the severely polluted threshold of 300.
Officials said air quality was due to improve overnight as a cold front arrived and should be better today, with lightly polluted forecast on the AQI.
This week is set to be wet and chilly, with a high of 11 degrees today.