Australia's biggest city, Sydney, has been engulfed in reddish dust blown in by powerful winds from the deserts of the country's outback. Visibility is so bad that international flights have been diverted and harbour ferry traffic disrupted. New South Wales and Queensland are also hit by the dust storms.The story was the same in the Hunter Valley, Wollongong, and in areas further west around Broken Hill. Emergency services reported a surge in calls from people suffering breathing problems. Children and the elderly have been told to stay indoors.