Shanghai's air quality is currently moderately polluted by PM2.5 particles blown from northern China, weather authorities say.

A weak westerly and north-westerly wind above the city is worsening the situation, the Shanghai Environmental Monitoring Center said.

The air quality index stood at 189 as of 7am Wednesday morning, with the one-hour concentration of main pollutant, PM2.5 particles, hitting 142 micrograms per cubic meter, according to the center.

The Liangcheng monitoring station in Hongkou District recorded an AQI reading of 203, or heavily polluted.

The pollution is forecast to linger in the city until Wednesday night, and rains expected for Thursday are likely to relieve the situation, forecasters said.

This bout of pollution started on Tuesday afternoon, the air quality index soared to 176 on 11pm that day.