BEIJING — Beijing will implement a series of temporary measures to stop construction and close heavy industries, all aimed at cleaning the city's notoriously polluted air when the Olympics begin in four months.

All digging and pouring of concrete on construction sites will be suspended from July 20-Sept. 20, the city's Environmental Protection Bureau said.

Nineteen heavy-polluting companies also have been told to cut their emissions in the same period by a further 30 percent.

Pollution — in addition to the violence in Tibet and other human rights issues — has been a major concern for China before the games. The International Olympic Committee has said it will postpone outdoor endurance events of more than one hour if the air quality is poor.

The Capital Steel Group in west Beijing has been told to reduce emissions, and production will be halted at the Eastern Chemical Plant of Beijing Eastern Petrochemical Co. Coal-burning boilers that fail to meet emission standards will also be shuttered.

Du Shaozhong, deputy director of the environment body, said production would be stopped at cement plants, concrete mixing plants and cement grinding plants in southeastern Beijing. Quarrying operations will also be stopped.

Du said specific details to remove vehicles from Beijing's streets would be announced later. Officials are expected to ban about half of Beijing's 3.3 million vehicles during the Aug. 8-24 Olympics.

The environment body said gas stations, oil depots and tanker trucks would cease to operate unless they were equipped with "oil vapor recovery" technology. Outdoor spray-painting will also be banned during the period, and "spraying or painting with harmful solvents will be temporarily banned."

Du said even more "strident" measures would be taken during the 17-day games "in case of extremely negative meteorological conditions." Hot, humid and stagnant air often settles over the city in August.

Five provinces and municipalities surrounding Beijing will also be shuttering factories, although their plans were not released. They are: the city of Tianjin; Hebei, Shanxi and Shandong provinces; and the huge Inner Mongolia region.

Beijing is one of the world's most polluted cities. A mix of particulate matter, carbon monoxide, sulfur dioxide and nitrogen dioxide often blankets the city at levels five times higher than World Health Organizations safety standards.

Beijing was covered in a moderate level of smog as Du made the announcement.

An IOC study released last month said that competition conditions would "not necessarily (be) ideal at every moment," but said Beijing's air quality was better than expected.

IOC president Jacques Rogge said earlier this month that the city's pollution will not endanger the athletes' health, but he's acknowledged performance levels might be "slightly reduced."