And while people with underlying lung disease were most at risk, he said it was likely that the air quality would cause problems for everybody.

"People with underlying chronic lung disease and people with allergies are going to find the conditions difficult but in fairness, an exposure to high levels of dust like this is going to cause difficulties for everybody, and people should be minimising how much time they are spending outside and should not be doing heavy exercise," Dr Wark said.

"Smokers may need to be aware of this as well because they will often have degrees of lung disease which they are not aware of.

"When you inhale this degree of dust it causes direct inflammation in the lower airways and extra mucus production as well, increasing the risk of chest infection and worsening of existing disease.

"The risks can persist for days after an event like this. The very small particles are the ones that can get down into the airways and cause problems, and what is attached to those particles."

His warning echoed that of NSW Health, which advised people to stay indoors due to the hazardous air quality.

"Children, older adults and people with heart and lung conditions are most susceptible to the effect of particle pollution," a NSW Health statement said.

"Fine dust particles can irritate the lungs of even healthy adults so everyone should cut back, significantly, on outdoor physical activity for the duration of the dust storm."

Vigorous physical activity should be minimised, indoors as well as outdoors, the statement said.

GP Access chief executive Dr Mark Foster said he anticipated high levels of activity at after-hours GP Access clinics last night as people struggled to cope with the effects of the air quality.

Newcastle Basketball Stadium was closed from 5pm yesterday due to the effect of the dust storm on the venue's air quality and surfaces.

Newcastle Basketball general manager Ivan Spyrdz said he was greeted by a "red snow dome-like" environment when he opened the basketball stadium yesterday morning.

All games were postponed, with tomorrow's semi-finals to proceed as scheduled, pending weather conditions.