Bureau of Meteorology forecaster Anita Pyne told news.com.au the peak of the storm would hit Sydney this afternoon — and there is already a "red haze" effect in Canberra.
She said it was still unknown how severe the storm in Sydney will be, but added she couldn't rule out a "major event" like the city's spectacular 2009 dust storm.
"It's going to be very windy and unpleasant later today, but the system is going to be moving east into the ocean and clearing overnight," she said.
"There is already a red sky effect in Canberra this morning, with potential for showers today, which could potentially clear the air."
Forecasters told the Australian the massive storm has now swelled to "the size of Tasmania".
NSW Health has issued a warning ahead of the Sydney storm's peak later today.
Director of Environmental Health Dr Richard Broome said it was especially important for children, older persons, and people with chronic respiratory and cardiovascular conditions such as asthma, chronic bronchitis, emphysema and heart disease to limit their time outside and not engage in vigorous exercise during a dust storm.
"If possible, stay in airconditioned premises where filtration systems can help to reduce dust particles in the air," Broome said.
"Dust may aggravate existing heart and lung conditions and cause symptoms like eye irritation and cough.
"Symptoms can occur for several days after dust is inhaled, so people with the chronic conditions need to be vigilant with their treatment programs.
"People with asthma or a lung condition who develop symptoms such as shortness of breath, coughing or wheezing, should follow their Asthma or Chronic Obstructive Pulmonary Disease (COPD) Action Plan."
Forecasters are closely monitoring a system headed towards the state and associated high winds that could pick up masses of loose dust caused by drought conditions.
"The strong winds associated with this dry soil, with a lack of vegetation, are the perfect conditions to pick up the dust, lift it up into the atmosphere and bring it east with the winds," Pyne said. "If it does happen it could have big impact. Dust storms can affect transport and even stop planes from landing."
An Airservices Australia spokesman said Sydney airport has advanced procedures to allow for landing and taking off in low visibility conditions.
However, if conditions were to worsen there is potential for flight delays. Parts of the state have already experienced dust storms this week with Griffith in southwest NSW covered by dust on Tuesday.
It's unknown if the weather event will be as severe as the 2009 Sydney dust storm but warnings will be issued if that is the case.
"We really have to wait and see," Pyne said.
It comes after an awe-struck pub owner captured the moment an insane dust storm "blew away" her outback town on Tuesday.
Olivia Probyn, the manager of the White Cliffs Hotel, in the remote town of White Cliffs in northwest NSW, said one moment the tiny outback community was going about its day, and five minutes later it was cloaked in an eerie blanket of red dust — obscuring everything in sight.
She said it descended on the town unexpectedly yesterday, after locals spotted it brewing in the distance five minutes before it struck.
"It was incredible, everything turned red and it just blew the town away," she told news.com.au. "It was so thick that I couldn't even see the corner shop across the road. It was that bad."
Probyn said it's the second major dust storm to lash the town this month after another similar occurrence on Melbourne Cup day.
"They don't hit often, but when they do they hit hard," she said. "It was spectacular and I didn't know what to do after.
"Everything was covered in dust and it was getting in through the cracks in the building because it's quite an old pub, the tiling was covered in thick mud so there was a big clean-up."
Probyn uploaded dramatic footage of the storm onto Facebook and within hours it had racked up thousands of views from users who left comments expressing shock and gratitude they weren't caught in the wild storm.
"Yikes!!," wrote one commenter. "Thank goodness we didn't have to go through this that night we went to White Cliffs."
The conditions are looking similar to those that led to the Sydney dust storm of September 2009, which blanketed Sydney as well as the rest of NSW.
There were more than 130 calls for help due to breathing difficulties, re-routed flights and smoke alarms ringing across the city as the wild storm hit nine years ago.
It was so bad, that it inspired Oscar-winning Blade Runner 2049 cinematographer Roger Deakins' post-apocalyptic, dust-filled version of Las Vegas in the 2017 sci-fi blockbuster.
