Booming car ownership is one factor behind Beijing's high levels of pollution [EPA]

The mayor of Beijing has warned that the city faces an "arduous" task ahead as it battles to curb pollution ahead of the Olympics later this year.

Speaking to the city legislature Guo Jinlong said authorities would introduce tough new emissions standards and blamed poor city governance among other issues for the low air quality.

"The task of bringing environmental pollution and traffic congestion under control remains arduous," Guo said.

Last year Jacques Rogge, the president of the International Olympic Committee, warned that some endurance events such as the marathon could be postponed or cancelled if pollution in the city is not significantly reduced.

Cancellation of Olympic events due to pollution would be a big embarrassment [AFP]

That would be extremely embarrassing for Chinese organisers of the games who have trumpeted the event as a showcase for the modern face of China.

With just 200 days to go until the opening ceremony, most of the venues are now ready but organisers still face a major challenge in cleaning up Beijing's skies.

Organisers have promoted the games as "green Olympics" and made much of the slogan and song "We Are Ready".

But despite a series of measures aimed at reducing emissions, residents of the Chinese capital say pollution levels have remained largely unchanged and the city is frequently blanketed in a thick smog.

Last week, state media reported that Beijing schools would cancel outdoor sports activities on smoggy days this year as a  health precaution.

Officials have pledged clean skies for the Olympics and say they have banned new construction projects, will shut down factories and even introduce limits on car usage if necessary to ensure those promises are kept.