Shanghai's air quality over the weekend is expected to see little improvement to the poor conditions experienced since Monday.
The hazy weather that began to smother the city at the beginning of the week should last for another three days, city forecasters said.
Zhu Jiehua, a chief service officer at the Shanghai Meteorological Bureau, said the absence of wind meant that pollutants in the air were not being dispersed quickly enough.
The bureau issued a yellow haze alert, lowest of a three-tier system, at 1:42pm yesterday reminding residents to stay indoors or wear masks if going out. Visibility was limited to 3,000 meters. It was the city's first haze alert since June 2011.
The city's air quality index was at "heavy pollution" level, second highest in a six-level scale, all day yesterday, according to the Shanghai Environmental Monitoring Center.
The PM2.5 figure - indicating tiny airborne particles 2.5 micrometers or less in diameter - has remained high since Wednesday night.
It was above 160 micrograms per cubic meter on Wednesday night and peaked at about 250 to 260 at 2pm and 3pm yesterday. At midnight it was 227.3 and the average over the previous 24 hours was 201. China's national standard is 75.
The haze was caused by the pollutants brought by a cold front from the north as well as airborne particles in vehicle and industry emissions, Zhu said.
To combat the problem of vehicle emissions, one of the major pollutants in the city, the local environmental watchdog said it may introduce National Emission Standard V, equivalent to the strict Euro V standard, in the second half of this year, while higher quality gasoline and diesel will be available.
Restrictions on and the elimination of highly polluting cars will also be further carried out this year, officials from Shanghai Environmental Protection Bureau said.
Beijing adopts the national V standard from next month.
Temperatures in Shanghai should be stable over the weekend with lows around 2 degrees Celsius and highs around 9.
Doctors are advising people with heart disease or respiratory problems and children and the elderly to stay indoors on heavily polluted days. They say it could be useful in such weather to eat fruits high in vitamin C like oranges and rinse the mouth and nasal cavities after returning home.
Ferry services to Chongming Island were canceled yesterday afternoon at about the same time as the haze alert was issued, maritime administration officials said. Three out of the past four days have seen the closure of local ferry ports.
Shanghai's two airports also suffered, with flights delayed as visibility dropped to around 2,200 meters.
Shanghai traffic authorities fear the bad weather is likely to cause problems tomorrow with the start of the Spring Festival travel peak.
Vehicles were already moving slowly on elevated roads and bridges during rush hour yesterday, traffic police said.
Qin Yun, a deputy director with Shanghai construction and transport commission, said the bad weather would "make the road traffic more fragile."
He added: "We advise drivers to plan routes ahead to avoid easily congested road sections and choose public transport."