International flights into Sydney have been diverted following a freak outback dust storm that has shrouded much of eastern Australia in a dramatic red glow.

Ferries from the harbour have also been suspended and motorists warned not to take special precautions due to a dramatic drop in visibility.

The storm started in the mining town of Broken Hill on Tuesday before sweeping east. It was caused by a major cold front whipping up the dust from the drought-stricken hinterland.

The gale force winds - measuring in excess of 60mph - also fanned bush fires in the state. By noon on Wednesday the storm, carrying an estimated 5 million tonnes of dust, had spread to the southern part of Queensland.

The dust storms stripped valuable topsoil from farmlands. At one stage up to 75,000 tonnes of dust per hour was blown across Sydney and dumped in the Pacific Ocean.

‘We’ve got a combination of factors which have been building for ten months already - floods, droughts and strong winds,’ said Craig Strong from DustWatch at Griffith University in Queensland.

‘Add to these factors the prevailing drought conditions that reduce the vegetation cover and the soil surface is at its most vulnerable to wind erosion.’

Health authorities, meanwhile, have urged people with asthma or breathing difficulties to stay indoors. The official air quality index for New South Wales recorded pollutant levels as high as 4,164 in Sydney. A level above 200 is considered hazardous.

Sydney residents told local radio that they woke to scenes from a Hollywood disaster movie, while many contacted emergency services fearing a major bush fire in the city.