Haze returns to Beijing, China unveils back-up pran:

BEIJING (AFP) - China on Thursday unveiled a string of emergency measures it was prepared to use in its battle to tame Beijing's stubborn smog ahead of the Olympics, as the city was again shrouded in haze.

Chinese authorities may close more factories, further reduce the number of cars on the road in the city and neighbouring areas, and stop all construction, the ministry of environmental protection said on its website.

"When there are extremely unfavourable weather conditions, there will be some emergency measures," the statement said.

Beijing has already taken drastic steps to reduce pollution, amid concerns expressed from as high up as International Olympic Committee president Jacques Rogge that the poor air quality could be detrimental to performance and health.

In the most dramatic anti-pollution measure, one million of the city's 3.3 million cars were taken off the roads from July 20, and more than 100 heavily polluting factories and building sites were closed down.