Asthma and respiratory diseases specialist Dr Peter Wark said inflammation in the airways caused by exposure to the dangerous levels of air pollution created by the storm was likely to linger.

"There's two issues, one is that the levels [of particulates in the air] were extraordinarily high on Wednesday, and they are likely to remain very high for quite a few days because of the amount of dust and the winds that are still around," Dr Wark said.

"The second thing is the exposure people would have had would also cause a response, which would lead to lower airways inflammation and extra mucus.

"Just that one-off exposure can be sufficient to cause ongoing problems for the next several days so people with lung disease may have deteriorated lung function and find that they need to use medication, and it's also possible they are more prone to developing chest infections so they need to be aware of that.

"I would still recommend that people with lung disease at least not exercise outside and minimise their exposure, and if they are having persistent symptoms that are not settling down then they need to see somebody."

The advice from NSW Health yesterday was that in general, people could return to their normal activities yesterday.

It is clear that people either took the advice to stay home, or called an ambulance for assistance, with no extra activity generated at the region's emergency departments, Hunter New England Health said.

The dust storm put pressure on the NSW Ambulance Service, prompting 462 calls for help from people experiencing breathing difficulties, 180 from the northern division which takes in the Hunter region up to the Queensland border.