Skies slowly returned to blue across NSW after a day that dawned dark red with thousands of tonnes of dust swirling in the air, playing havoc with transport and threatening health.
Ferries were cancelled on Sydney harbour, flights were diverted away from Sydney airport and health authorities warned residents across the state to stay indoors and avoid vigorous exercise on Wednesday.
Air particle pollution was hundreds of times higher than normal as a cold front moved across the state, picking up dust from paddocks desiccated by drought.
Up to 75,000 tonnes of dust per hour was blown into the waters off the coast and particle pollution was the highest on record - over 15,000 micrograms per cubic metre at times, when a normal day would see less than 20 micrograms.
The choking dust was far thicker than bushfire smoke, which commonly contains about 500 micrograms per cubic metre.
Sydney delivery driver Aaron Ahn was wearing a face mask and had trouble breathing.
"The dust is everywhere in the wind," he said.
"It is harder to breathe when I'm walking outside and I get a bit dizzy."
NSW Health warned children, elderly people and those with heart and lung conditions to avoid outdoor activities, and said all vigorous physical activity should be minimised - even indoors.
Concern for the health of horses forced the cancellation of racing at Sydney's Canterbury racecourse, and later at Brisbane's Eagle Farm, as the dust storm moved across the border into Queensland.
The problems began on Tuesday when an intense low-pressure system formed over southern NSW and gale force winds on its northern edge developed during the afternoon.
"The winds whipped up a great dust cloud and that's been transferred across the whole of the state," the Bureau of Meteorology's regional director Barry Hanstrum told AAP.
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Early on Wednesday, the dust hit Sydney, which woke to a blood-red dawn, fading slightly to orange as the sun rose higher in the sky.
And everywhere there was dust. It coated footpaths, shop floors, train stations and any other surface the wind could penetrate.
Cityrail trains carried it through tunnels and into underground stations.
"When I got on the train at Cronulla all our seats were covered in this red dust," Robyn Jaques said.
"It's got over all of my clothes so they'll need to be cleaned."
For city dwellers, the dust storm was a temporary nuisance, but in rural areas the effects would be long-lasting.
Stephen Cattle, a soil scientist and dust expert at the University of Sydney, said nutrient-rich topsoil was being blown off farming properties.
"They're looking at a loss in the potential productivity of their topsoil," Dr Cattle told AAP.
"They're losing part of their resource of their land and it's not something that is easily restored."
Emergency services were kept busy across the state, with the NSW Ambulance Service responding to calls from more than 300 people with breathing difficulties.
Firefighters received 10 times the usual number of emergency calls, with NSW Fire Brigades spokesman Superintendent Graham Kingsland saying the dust triggered about 600 fire alarms, which all had to be investigated.
In addition, there were about 400 triple-zero calls, some from people who mistook the red dust for fires, and others relating to wind damage and trees fallen on power lines.
By late afternoon, the unusual weather system had pushed into Queensland, returning the Sydney sky to its normal colour.
The Bureau of Meteorology said it was highly unlikely Sydney would see a repeat of the rare dust storm any time soon.
"There's a southwesterly change coming through and that's what's been blowing most of the dust away," duty forecaster Steph Spackman said, adding that weather pattern would continue on Thursday.
The Weather Channel said clearing conditions across the east coast of the country should see a reasonably fine and dry day on Thursday, with a top temperature of around 23 degrees and easing winds.
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