Beijing and its co-host Olympic city Hong Kong have been blanketed in smog in the countdown to the Games which open in 10 days.
Despite years of efforts to rid the Chinese capital of its notorious pollution and a raft of recent attempts at quick fixes, a thick haze has cut visibility across Beijing to a few hundred metres.
Last week Beijing ordered more than a million of the nation's 3.3 million cars from the roads and closed dozens of polluting factories, apparently with little impact.
The state-run China Daily newspaper says the government may ban 90 percent of private cars and close more factories.
But the Games organising committee remains confident that athletes will have little to worry about regarding pollution.
In Hong Kong, which will host the equestrian events, the city's air pollution level has been classified as high.