Beijing is considering even tougher restrictions on cars, banning 90% of them from the roads in a desperate attempt to clear the city's air in time for the opening of the Olympic Games on 8 August.
Despite years of efforts to rid the Chinese capital of pollution and a number of recent attempts at quick fixes, a thick layer of smog has cut visibility across the capital to a few hundred metres.
Last week, Beijing ordered more than a 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% of private cars and close more factories.
But the Games organising committee remains confident that athletes will have little to worry about regarding pollution.
Hong Kong will host the equestrian events. The city's air pollution level is classified as high.
The Australian Olympic Committee says the poor air quality is a worry but no great surprise.
Australian competitors are being given the option of pulling out if they are concerned about air quality, but spokesperson Craig Phillips says it is unlikely any of the 433-strong contingent will do so.