Beijing - The Beijing government put in place emergency measures Wednesday to try to combat thick smog that has encased the city, which the Communist Party has hailed as a showcase capital, in brown and gray soot. The measures include temporarily shutting down more than 100 factories and ordering one-third of government vehicles off the streets, according to official news reports.

The effort came on the second straight day of air that is rated "hazardous" by the standards of the U.S. Environmental Protection Agency. That rating, in which the air quality index surpasses 300, means people should not venture outdoors at all. This month, Beijing has writhed in the grip of the most polluted air days on recent record. The surge in pollution, which is happening across northern China, has angered residents and led the state news media to report more openly on air quality problems.

Officials have also begun acknowledging the severity of the air pollution. Xinhua, the state news agency, reported that Wang Anshun, the newly appointed mayor of Beijing, said Monday that the government had come up with a preliminary plan to curb the pollution.

"I hope we can have blue skies, clean water, less traffic and a more balanced education system," Wang said at a session of the municipal legislature.

Wang also told lawmakers that "the current environmental problems are worrisome." He said the number of vehicles in Beijing should be allowed to increase, but slowly. The Xinhua report said there were an estimated 5.18 million vehicles in Beijing, compared with 3.13 million in early 2008.

Wang told the legislature on Jan. 22 that the Beijing government was aiming to cut the density of major air pollutants by 2 percent this year. To that end, officials are ordering 180,000 older vehicles off the roads, promoting the use of "clean energy" for government vehicles and heating systems, and growing trees over 250 square miles of land in the next five years, Xinhua reported.

Prime Minister Wen Jiabao also addressed the air pollution at seminars on economic development in the past week, Xinhua said. Wen said efforts should be made to "optimize industrial structure, promote energy saving and emission reduction and advance ecological progress," it said.

On Tuesday morning, the air quality index as measured by a device atop the U.S. Embassy in central Beijing reached 517, which was so high that the rating was labeled "beyond index" on an embassy Twitter account, @BeijingAir. (Once before, the account had labeled a rating of more than 500 "crazy bad," but embassy officials quickly deleted that tweet.) Index readings on a website run by the Beijing government had similar numbers.

The indexes are based primarily on measurements of a potentially deadly particulate matter called PM 2.5. In mid-January, some monitoring devices set up by the government in the Beijing municipality recorded PM 2.5 concentrations of nearly 1,000 micrograms per cubic meter, which was on par with the worst days in industrial London during the mid-20th century.

Beijing announced in early 2012 that it would report PM 2.5 levels, in response to an outcry from residents demanding the information. A total of 74 Chinese cities are supposed to release that data this year. Among the prominent voices calling for greater disclosure is Pan Shiyi, a real estate tycoon.

This week, Pan has been asking the 14 million followers of his microblog whether China should adopt a "clean air act" that would be much stronger than current laws. As of Wednesday afternoon, 99 percent of the more than 42,000 replies had voted in favor of the act.

"In order to control air pollution, we need everyone to participate," Pan wrote. "The most important thing is legislation."

Pan did not give details on what the legislation would say. He said that as a member of the Beijing municipal people's congress, he would bring up the idea of an act to other legislators and officials. In China, though, legislatures have little power; senior party officials make important policy.

Zhang Xin, Pan's wife and business partner, said on her microblog that after thousands of people died as a result of air pollution in Britain in the 1950s, the government vigorously tackled its air quality problems with strict laws.