A thick line of dust that has smothered much of New South Wales and Sydney has caused air quality to reach a “hazardous” level with another wave of dust set to come, leading to a spike in calls for help from people with breathing difficulties.

Strong winds from a low pressure system have whipped up masses of dirt across the drought-stricken state, which headed towards the coast on Thursday.

The storm stretched more than 500km from the Victorian border, through Canberra and up towards Queensland.

Bureau of Meteorology senior meteorologist Simon Louis says more dust is expected to be pushed to the coast late Thursday night or early Friday morning.

He said the dust should not be underestimated despite its grey, hazy appearance with the majority coming from lake beds in South Australia.

“Even though it may not have looked quite so red and spectacular (as 2009) the air quality has dropped significantly,” Louis told reporters in Sydney.

Bureau of Meteorology duty forecaster Anita Pyne said it was a “huge system.”

It was not uncommon for inland parts of NSW to experience small-scale dust storms but one this size was “unusual”, she said.

“It’s unusual for dust events to happen on the coast because we’re so much further away from that dust over the western NSW basin and we’ve got the Great Dividing Range in the way.”

It’s expected the dust will keep sweeping east and may not clear the coast until Friday.

Satellite view showing the dust storm moving across the New South Wales. Photograph: Bureau Of Meteorology/AAP

NSW Ambulance Assistant Commissioner Tony Gately said there had been a “significant peak” in call outs with 90 people needing assistance due to asthma or breathing difficulties on Thursday morning.

Extra paramedics and call takers have been put on to meet the demand with up to eight calls coming in every hour.

“Anyone prone to respiratory distress needs to be absolutely vigilant,” Gately said in a statement.

The dust storm is moving through #NSW. This photo taken in the Blue Mountains moments ago by @RFSCommissioner. Expected to reach the coast over the coming hours. #dust #drought2018 pic.twitter.com/kzxmQYek3f — NSW RFS (@NSWRFS) November 21, 2018

Heading south from Sydney the #duststorm now blanketing the Sydney basin, The Royal National Park and this is the current view of Wollongong and looking back up the coast north to the Royal National Park @abcnews @abcsydney pic.twitter.com/udXtJSus1C — Rory Macdonald (@Rorymacabc) November 21, 2018

“This warning cannot be underestimated, conditions like asthma can be deadly and to take risks in the current conditions would be very ill advised.”

NSW Health has urged children, older people and those with respiratory conditions to take extra care.

Students at public schools in areas covered by the NSW Health advice were being kept indoors and were not to engage in vigorous exercise, a spokeswoman from the education department confirmed.

Environmental health director Richard Broome said people should stay inside as much as possible due to the air quality between Sydney and the Hunter reaching a “hazardous” level.

“It’s important for the rest of the day people should be cautious,” he told reporters in Sydney.

He said dust particles can get very deep into people’s lungs and cause heart and lung conditions, asthma and emphysema to worsen.

The NSW Institute of Sport advised coaches and athletes to reconsider conducting training sessions outdoors in Sydney on Thursday.

.@NSWHealth have put out a Health Risk Alert due to the potential of a dust storm over the Sydney Metropolitan area. Coaches & athletes should consider the potential risk when undertaking training sessions outside today #TeamNSWIS pic.twitter.com/Xfhl49PTah — NSWInstituteOfSport (@theNSWIS) November 21, 2018

The gusty winds which brought the dust have also affected flights at Sydney Airport with up 40 departing flights cancelled and delays across all airlines.

The Sydney Airport tweeted on Thursday afternoon both international and domestic flights have been affected as they are forced to operate on a single runway due to the weather.

Meanwhile, snow was forecast for parts of the Snowy Mountains above 1,100 metres.

“Everything’s happening,” Pyne said.

The dust is starting at Sydney airport. Thanks to my son for the photo. #duststorm pic.twitter.com/c7jSYsrD8X — Jenny Woodward (@jennyweather) November 21, 2018

One talkback caller said the sky around the Blue Mountains looked as though there was an eclipse.

“It’s just crazy – I’ve never seen it like this before,” he told Sydney’s 2GB radio. “It’s getting worse. You can barely see 500m past the valley.”

However some Sydneysiders have been rather unimpressed by the storm – so far.