Thick, off-the-scale smog shrouded eastern China for the second time in about two weeks Tuesday, forcing airlines to cancel flights because of poor visibility and prompting Beijing to temporarily shut factories and curtail fleets of government cars.

The capital was a colorless scene. Street lamps and the outlines of buildings receded into a white haze as pedestrians donned face masks to guard against the caustic air. The flight cancellations stranded passengers during the first week of the country's peak, six-week period for travel surrounding the Chinese New Year on Feb. 10.

The U.S. Embassy reported an hourly peak level of PM2.5 — tiny particulate matter that can penetrate deep into the lungs — at 526 micrograms per cubic meter, or "beyond index," and more than 20 times higher than World Health Organization safety levels over a 24-hour period.

Liu Peng, an employee at a financial institution in Beijing, said he will keep his newborn baby indoors.

Ng Han Guan/AP

A man wears a mask as he walks through the thick haze on Beijing's Tiananmen Square on Jan. 29.

"It's really bad for your health, obviously," Liu said. "I bike to work every day and always wear a mask. The pollution in recent years is probably due to the increase in private cars and government cars."

Visibility was less than 100 yards in some areas of eastern China, the official Xinhua News Agency reported. More than 100 flights were canceled in the eastern city of Zhengzhou, 33 in Beijing, 20 in Qingdao and 13 in Jinan.

Petar Kujundzic/Reuters

Cars drive along a street on a hazy day in Beijing on Jan. 29.

Every year, China's transport system bursts at the seams as tens of millions of people travel for the Lunar New Year holiday, in the world's largest seasonal migration of people.

Ren Haiqiang, a bank worker in his early 30s, said he had booked tickets to fly out of Beijing on Thursday to visit family in the coastal city of Dalian, but now worried about flight cancellations.

"Traveling over the holiday is already a huge hassle, along with all the gift-giving and family visits. We thought flying would be the best way to avoid the crush, but if the weather continues like this we'll be in real trouble," Ren said as he waited in line at a bakery in downtown Beijing.

Beijing's city government ordered 103 heavily polluting factories to suspend production and told government departments and state-owned enterprises to reduce their use of cars by a third, Xinhua said. The measures last until Thursday.

Beijing's official readings for PM2.5 were lower than the embassy's — 433 micrograms per cubic meter at one point in the afternoon— but even that level is considered "severe" and prompted the city government to advise residents to stay indoors as much as possible. The government said that because there was no wind, the smog probably would not dissipate quickly.

Patients seeking treatment for respiratory ailments rose by about 30 percent over the past month at the Jiangong Hospital in downtown Beijing, Emergency Department chief Cui Qifeng said.

"People tend to catch colds or suffer from lung infections during the days with heavily polluted air," he said.

Air pollution has long been a problem in Beijing, but the country has been more open about releasing statistics on PM2.5 — considered a more accurate reflection of air quality than other pollutants — only since early last year. The city hit its highest readings on Jan. 12, when U.S. Embassy readings of PM2.5 reached as high as 886 micrograms per cubic meter.

Celebrity real estate developer Pan Shiyi, who has previously pushed for cities to publish more detailed air quality data and who is a delegate to Beijing's legislature, called Tuesday morning for a "Clean Air Act." By late afternoon, his online poll had received more than 29,000 votes, with 99 percent in favor.

On Monday, Wang Anshun was elected Beijing's mayor after telling lawmakers the municipal government should make more efforts to fight air pollution, according to Xinhua.

Last week, he announced plans to remove 180,000 older vehicles from the city's roads and promote government cars and heating systems that use clean energy.