Lower Hunter air quality has at times rivalled that of the most polluted parts of the world during the past week.

The Lower Hunter air quality index hit 647 at 4pm on Wednesday - the safe range is under 100.

Hunter New England Health Emergency departments have also had a 30 per cent increase in presentations for respiratory conditions, such as asthma, compared to the same time last year.

Maitland Hospital experienced a spike in people presenting with asthma and other breathing problems - 26 in total last week compared to the five year average of 20.

Public health physician Dr David Durrheim said the current air quality situation is too dynamic to be able to predict when the region will get a reprieve.

"It is certainly the worst we have seen since the installation of the Lower Hunter air quality monitoring network," Dr said. "What is particularly concerning is the is amount of fine particle pollution (PM2.5) which can get into the lungs."

"The only thing that will lead to an improvement are massive showers of rain to extinguish the fires and to settle down all these particulates," he said.

"People, particularly those with asthma, respiratory or heart conditions, need to monitor conditions and take appropriate action. People need to be guided by the rural fire service in the first instance.

"Because the fire situation is so dynamic those high risk groups must limit their amount of outdoor activity and stay indoors with the windows and doors firmly closed," Dr Durrheim said.

Dozens of events across the region have been cancelled including sport and outdoor Christmas activities.

Telarah Public School called off its swimming carnival on Friday and Maitland Football Club's Skill Acquisition Program called of Thursday afternoon training. Cessnock's Carols in the Park scheduled for Friday night were also cancelled.

And the health warnings extend to animals too. RSPCA NSW spokesperson Sharon Andronicos said if it is uncomfortable for a human to breathe, then it is uncomfortable for pets too.

"I would suggest not doing strenuous activities or big walks until the smoke clears," she said.

"If possible bring your pets inside and keep them cool and offer plenty of water.

"Pets with pre-existing respiratory conditions such as asthma or brachycephalic breeds may be at an increased risk," she said.

Brachycephalic breeds have condensed snouts that often cause respiratory distress.

These include Pugs, British Bulldogs, French Bulldogs, Boston Terriers, Shar-Peis, Persian cats and Exotic Shorthair cats.