Thick, choking smog enveloped cities in northeast China on Tuesday, closing schools and airports, snarling traffic and reducing visibility to a few yards, in a dramatic sign of the country’s worsening air quality.

China’s breakneck dash for economic growth has badly damaged the environment, and the rapid deterioration in the country’s air and water quality has increasingly become a source of public unrest. As a result, improving environmental standards has become a priority for the government. But the acrid clouds enveloping several cities this week showed how tough that task has become.

In the industrial city of Harbin, home to more than 10 million people, vehicles crawled through the smog with fog lights on or emergency lights flashing. Bus service was canceled, a major highway was closed and hospital admissions soared by 30 percent, local media reported.

The smog descended on Harbin on Sunday evening. On Monday, the measurement of fine particulate matter in the air known as PM2.5 reached 1,000 micrograms per cubic meter in parts of the city, 40 times what the World Health Organization considers safe.

That was even higher than the levels recorded during Beijing’s “airpocalypse,” when a dense, yellow smog cloaked the capital city for several days in January. The Washington metro area’s PM2.5 level on Tuesday was 12.6 micrograms per cubic meter.

On Monday, visibility was so low in Harbin, about 780 miles northeast of Beijing, that two city buses got lost while plying their regular routes. Pedestrians wore masks or placed their hands over their faces as a precaution.

“I did not even dare to cross the street,” said Zhang Xiaofeng, a 24-year-old bulldozer driver, who complained of eye pain and coughing bouts because of the smog. “I waited and waited at the intersection and looked again and again, but I couldn’t see if any cars were coming. Even the traffic lights were invisible.”

On Tuesday morning, the level of fine particles in the air reached 822 micrograms per cubic meter. Although the air quality had improved by lunchtime, the fog descended again in the afternoon, residents said; primary and middle schools and the airport remained closed for a second day, though high schools reopened.

More than 250 flights were canceled Monday, according to state media.

“I can’t even see the apartment building next to mine, which is only 10 or 20 meters away,” said 42-year-old homemaker Li Li, contacted by telephone. “There is a food market in our compound: I know it is open because I can hear it, but I can’t see it. I’m not going out, and I won’t let my child go out.”

In the city of Changchun, which lies about 180 miles closer to Beijing by road, the level of fine particles peaked at 700 in some areas Tuesday, and the airport was closed for several hours.

Officials told local media that the smog in northeast China worsened after the government turned on its coal-fired public heating system Sunday. They also blamed straw-burning in villages at the end of the harvest season and a low-pressure weather zone that trapped the polluted air.

‘Weather made me panic’

Last month, China unveiled its most ambitious plan yet to reduce air pollution, calling for significant cuts in coal use in industrial regions in the country’s north and aiming to lower PM2.5 levels by 10 percent over five years. But with economic growth slowing, many commentators wonder whether local governments will want to bear the cost of cleaning up the environment.

Previous efforts to improve air quality have foundered because of poor implementation by local governments, which continue to protect heavy industries and tolerate widespread violation of environmental norms, according to Ma Jun, director of the Institute of Public and Environmental Affairs in Beijing.

“The central government has recognized the fundamental cause — which is its overuse of coal — and what sort of solution should be taken,” said Huang Wei, a campaigner with the environmental group Greenpeace in Beijing. But Huang said the government’s plan did not go far enough in addressing the problem across the entire nation. As a result, she said, “more and more places are going to have bad-air-quality days.”

On a Chinese microblogging, or weibo, site, one Harbin resident complained of having to walk to work through the smog with stinging eyes and a sore throat because the bus service was canceled and cabs were hard to find.

“The weather made me panic, I even wonder if human beings will become extinct or not,” she posted under the user name “AlwaysBelieveIn.”

“I live in a country making people desperate,” posted another weibo user. “The environmental pollution is not scary. What’s scary is the no-action government and the silence of people like slaves.”

Public health, political risks

A survey by the Pew Research Center published last month showed that the Chinese are increasingly worried about air and water quality, with air pollution nearly as big a concern as rising prices, corrupt officials and the gap between rich and poor. The Communist Party clearly worries that the issue is undermining its legitimacy in the eyes of many.

Beijing, routinely blanketed by a gray smog, recently made a “declaration of war” on air pollution. On Tuesday, it announced fresh measures to cope with the menace, saying the city would close schools and factories and further restrict car use — allowing only cars with odd- or even-numbered license plates to be operated at specific times — when pollution reaches “red alert” levels.

But Wang Tao, a climate and energy specialist at the Carnegie-Tsinghua Center for Global Policy in Beijing, said inadequate investment in public transportation and poor urban planning also mean that choking exhaust fumes are likely to remain a fact of life in the capital for a while.

Large-scale investments in heavy industries in the surrounding provinces, as part of a recent economic stimulus plan, mean that any cuts in coal use will also be hard to achieve. “It is quite difficult to see things getting better in terms of air quality in the short term,” he said.

Last Friday, American jazz singer Patti Austin was forced to cancel a concert at Beijing’s Forbidden City Concert Hall after being taken to a hospital “in an emergency” on suffering a severe asthma attack and respiratory infection, according to a statement on her Web site.

Air pollution increases the risk of acquiring lung cancer and respiratory and heart diseases.

Zhang Jie contributed to this report.