Shanghai Daily/Xinhua

Thick fog across northern China yesterday threw air and road transport into chaos and sent scores of people to hospital with respiratory illnesses.

More than 20 highways in the north were closed and visibility was reported to be as low as 500 meters in Beijing.

It was as low as 10 meters on some road sections in Tianjin, according to Zhao Jinghong, a forecaster with Tianjin Municipal Observatory.

The Beijing and Tianjin observatories both issued yellow fog warnings yesterday.

Police in both cities were called out repeatedly to deal with congestion and accidents.

Visibility at Beijing Capital International Airport fell to 600 meters, causing flight delays, especially to Shandong Province.

The airport launched an emergency fog plan to avoid mass congestion.

It increased intervals between flights and urged travelers to check times before going to the airport, an official said.

The pollutant index reached 249 at noon in Beijing, a level at which people are advised to scale back outdoor activities and go out with a respirator, said the local environment bureau.

The price of tomatoes rose from one yuan to 1.8 yuan a kilogram as vegetables from Shandong and Henan Provinces, two major suppliers to Beijing, were kept out of the city by the fog.

There were 30 percent more patients with respiratory infections than usual at major Tianjin hospitals.

Sections of five Beijing and eight Tianjin highways were closed after the fog came down on Sunday night.

The highway from Beijing to Shenyang, capital of northeastern Liaoning Province, reopened at 9:33am yesterday.

Ten highways closed in Liaoning had reopened by 2pm, but the provincial observatory warned of possible snow last night.

More than 40 flights from Taoxian Airport in Shenyang were delayed on Sunday.

The fog in eastern Shandong Province had thinned by noon yesterday and all highways except the Dezhou sections of the Beijing-Fuzhou highway reopened.

Five flights from the provincial capital's Ji'nan International Airport were canceled yesterday morning and all the other flights were delayed.

Six highways in northern Hebei Province were still closed yesterday.

Five flights were canceled and four delayed at the provincial capital's Shijiazhuang Airport.

The closure of highways left bus passengers for Baoding and Shijiazhuang, Hebei's two biggest cities, stranded in Liuliqiao bus station.

He Lifu, a meteorologist with the National Meteorology Center, said high humidity and little wind over the past week caused the fog.

The Beijing observatory said cold air late last night would bring fairly strong winds to north China and disperse the fog.