Sept. 23 (Bloomberg) -- An orange blanket of dust blown in from Australia’s Outback engulfed Sydney today, shrouding the Opera House with choking powder, snarling traffic and disrupting flights before swirling up Australia’s eastern seaboard.

“It’s like a nuclear winter morning,” tourist Peter Wilson, 53, said at Circular Quay in central Sydney as fog horns echoed across the harbor. “It is so eerie.”

The dust cloud, more than 500 kilometers (310 miles) wide and 1,000 kilometers long, was the largest to hit Sydney since the 1940s and was driven from the drought-stricken interior by gale-force winds, the Bureau of Meteorology said. The city’s skies returned to their usual blue by early afternoon as the storm swept through Brisbane, almost 1,000 kilometers north.

The Sydney Harbour Bridge was hidden by a thick haze as the early morning sun struggled to pierce the shroud of dust. Train commuters, some wearing masks or clutching handkerchiefs to avoid breathing in the particles, stood on platforms snapping photographs of the spectacle on their mobile phones.

The New South Wales state government said air quality in parts of the city was “hazardous” and advised schools to keep pupils indoors. Sports lessons were canceled for the day.

‘Incredible Event’

Strong winds caused by a low pressure system whipped up top-soil and dust parched by years of drought to cause this “pretty incredible event,” said bureau spokesman Rob Webb, adding the cloud was visible from space.

Australia is the driest inhabited continent on earth and the country’s inhabitants are accustomed to extreme weather. Record temperatures and gales earlier this year drove firestorms in the southeastern state of Victoria that left 173 people dead.

The cloying dust left many residents of Australia’s most populous city tight-chested with a metallic aftertaste in their mouths as they made their way to work through the haze.

“I haven’t seen dust storms like this since I was in China a few years ago,” said solicitor Jim Harrowell, 55, as he stood in Sydney’s financial district, where office windows were clogged with dust. “We’re lucky it’s not raining, otherwise there would be little red spots all over us.”

Yachts on the harbor, usually gleaming white, had a dull yellowy sheen. Drivers shuffled slowly over the Sydney Harbour Bridge, their windscreens smeared and filthy.

Flights Diverted

The storm caused “significant disruption” at Sydney Airport, with a total of 18 international flights diverted to Brisbane or Melbourne and six international flights canceled, the airport said in a statement. Flights overseas faced delays of as much as six hours, while domestic arrivals and departures had delays of up to three hours.

Qantas Airways Ltd., Australia’s largest airline, said its Sydney passengers experienced average delays of two hours and that it expected to clear the backlog by the end of the day.

The storm swept through Broken Hill in southwest of New South Wales yesterday afternoon. “It turned to night for a short time,” local police Inspector Grant Lister said by telephone. “What you got in Sydney was nothing.”

In the Hunter Valley wine-growing region north of Sydney, a fine dust settled on the grapes and vines today.

“When I woke up this morning it was something from the movies,” said Andrew Thomas of Thomas Wines. “It was glowing red, just amazing.”

The storm was Australia’s largest since October 2003 when about 16 megatons of dust was swept out to sea off the state’s southern coast, said Ross Mitchell, a scientist at the Commonwealth Scientific and Industrial Research Organization.

Asthma Sufferers

The New South Wales Ambulance Service said it experienced an increase in calls from asthma sufferers and some were taken to hospital.

Oakdale, in the city’s southwest, recorded a level of 1,719 on the Department of Environment’s air quality index. A reading of 200 and above is considered hazardous and people with heart or lung disease, the elderly and children were advised to avoid exercising outdoors.

The state Fire Brigade experienced a 10-fold increase on its usual call rate as the dust tripped automatic fire alarms and smoke detectors, spokesman Graham Kingsland said.

To contact the reporter on this story: Nichola Saminather in Sydney at nsaminather1@bloomberg.net; Ed Johnson in Sydney at ejohnson28@bloomberg.net.

Last Updated: September 23, 2009 03:37 EDT