The Beijing Municipal Maritime Administration said 108 cities across the country would take part in the no-car day with varying levels of enforcement, encouraging people to get back on their bicycles for which Chinese cities used to be famous.

"We are only advocating that small cars keep off the roads in certain districts," said a Beijing official surnamed Zhang.

Beijing embarked on a four-day experiment last month to see if taking 1.3 million cars off streets would substantially reduce pollution.

Beijing is closing down the worst-polluting factories and switching thousands of homes from coal to gas use but air quality remains the biggest concern for Olympic organisers.