A Sydney doctor has raised concerns about the health impact of awful air pollution as more than 100 bushfires burning across NSW cause "the longest and most widespread" period of poor air quality on record.
Northwestern Sydney GP Kim Loo, who works in Riverstone, says she's already dealing with the health impacts of bad air quality.
"I've had patients come in with nasal symptoms, sinus symptoms and sore throats," she told AAP on Wednesday.
"I've had a few patients coming in on bad air quality days just from breathing in the high levels of pollution."
Heavy bushfire smoke is currently smothering Sydney and other parts of NSW - and it's forecast to linger into the weekend. Conditions have been "hazardous".
The NSW environment department says this season's bushfire emergency has caused "some of the highest air pollution ever seen in NSW".
"NSW has experienced other periods of poor air quality that lasted several weeks, including the 1994 Sydney bushfires and the Black Christmas bushfires of December 2001 to January 2002," a spokesman said in a statement.
"This event, however, is the longest and the most widespread in our records."
The NSW Rural Fire Service on Wednesday said the "heavy smoke" would be noticeable in Sydney for several days.
Air quality was hazardous for large past of eastern and southwestern Sydney on Wednesday evening, as well as parts of the lower Hunter and Central Coast.
Dr Loo compared the impacts of breathing in the polluted air to "smoking without consent".
"With fine particulate matter, you are kind of smoking without consent, you have no choice about the quality of air you breathe," she said, adding the combined impact of air pollution and heat over summer would be "awful".
"Pollution is like a big soup of different particles. The problem is they are toxic particles."
The GP says regular air pollution from cars and coal-fired power stations is mixing with smoke from the fires.
Face masks are considered ineffective as they fail to filter out smoke particles.
Dr Loo, who is a member of Doctors for the Environment Australia, said the country's health system was not prepared for the health impacts of climate change such as complications caused by rising temperatures and poor air quality.
"The health sector is going to bear the brunt of the cost.
"Climate change will have a great impact on our health. These fires could be our new normal."
Australian Associated Press