Thick smoke blanketing parts of Australia's east could cause long-term health damage, with experts warning it will get worse if climate change isn't tackled.

Dangerous smoke choking Sydney could be causing long-term damage even to healthy people, with experts warning it will only get worse if climate change isn't tackled.

Thick, grey smoke has blanketed the harbour city and its outer suburbs for weeks as bushfires range on in the north, south and west of NSW.

In November, the city recorded 15 days of poor air quality and on Tuesday the levels of ultra-fine PM2.5 particles, small enough to enter the lungs and bloodstream, were more than 10 times the accepted safety level.

Hospitals have recorded a 30 per cent increase in admissions, indoor smoke alarms are being triggered and students are spending less time outside during recess and lunch breaks.

On social media, Sydneysiders continue to share images of the burning-orange sun, shrouded in haze, while many others complain about tasting and feeling a burning sensation in their throats.

People with lung or heart conditions, the young and old have been advised to stay indoors, but experts say healthy people should also be concerned.

"There are a number of long-term health impacts from air pollution and particularly high levels of PM2.5 which is what we're seeing in Sydney," University of Melbourne's Dr Gabriel da Silva, an atmospheric chemistry expert, told AAP.

A combustion and atmospheric chemistry expert, Dr da Silva said inhaling fine particles can lead to "increased incidences of chronic diseases, cancers and neurological illnesses".

Advice to stay inside is only effective for so long because air quality without ventilation deteriorates over time, he added.

Dr da Silva said as the climate continues to heat up, it's reasonable to expect the lingering haze as "the new norm and may get worse".

It's a view shared by Professor Bruce Thompson, a respiratory physiologist and research academic at Swinburne University.

"This should be a massive wake up call. Sydney's air quality is now in the top 10 worst in the world. In a country like Australia, how is this okay?" he told AAP.

He described the lungs as "made of tissue paper" and the more smoke inhaled, the increased likelihood more people will develop asthma.

Prof Thompson has been involved in the longitudinal study of the health risks associated with Victoria's 2014 Hazelwood mine fire, which burned for weeks and blanketed neighbouring towns in ash.

Since the mine fire, there has been an increase in emergency presentations and hospital admissions for respiratory diseases, he said.

"A similar project will need to be done in Sydney, but at the same time, we already know the consequences - how many times do you want to do the study?

"We just need to change and it's doable right now."

Prof Thompson likened the need for action on climate change and its impending health impacts to treating cancer.

"If a doctor said to you, 'We've found this mass we think it's a 10 per cent chance it might be cancer, which will kill you, I think we should take it out', are you going to go 'It's only a 10 per cent chance, there's a 90 per cent chance I'll be okay' - are you going to take that risk?

"Climate change is the other way round, we've got 90 per cent certainty that this is the problem," he added.