Sydney smoke at its 'worst ever' with air pollution in some areas 11 times 'hazardous' threshold
Sydney's air quality plummets from surrounding bushfires. (ABC News)
Sydney's air quality index (AQI) has reached as high as 11 times hazardous levels, due to bushfires on the city's outskirts.
This level of air pollution means everyone, regardless of their health, should cut back on outdoor physical activity, NSW Health said.
The worst reading is currently at Macquarie Park in Sydney's north-west, which recorded air quality of 2,214 between 9.00am and 10.00am this morning.
Parramatta North has reached 2,024, with levels continuing to rise.
Any region with an AQI over 200 is considered "hazardous".
The high readings are largely due to poor visibility, although particle levels are also well into hazardous territory in several locations.
The Rural Fire Service (RFS) headquarters in Homebush was briefly evacuated, after smoke alarms went off inside the building.
RFS Wollondilly Group Captain Dave Murray says the smoky conditions around the Green Wattle Creek blaze, south-west of Sydney, are expected to worsen into the afternoon as westerly winds pick up between 2.00pm and 6.00 pm.
He said the thickening smoke will likely become a problem for crews.
Parts of the state's Central Tablelands, north west, Hunter, Illawarra and south west regions are also experiencing dangerous levels of smoke.
Dr Richard Broome, from NSW Health, said people with respiratory conditions should avoid going outdoors.
"The people who are most vulnerable are people who have existing heart and lung problems," he said.
While smoke has been near-permanent fixture in Sydney this bushfire season, people took to social media today to lament the "worst" air quality they had seen.
"I've never seen Sydney like this before," Lisa Herbertson said on Twitter.
"Woke up this morning to the worst smoke haze I have ever seen in our local area," Samantha Waterfield in Belmont North said.
"Definitely the worst the conditions on the Northern Beaches have been. I've had no voice for three days from the smoke, I can't imagine how people living closer are coping," Kelly Owens said on Twitter.
The Bureau of Meteorology (BOM) said there would be clearer skies later thanks to a wind change.
that is also when the extreme heat will hit, with temperatures forecast to reach 42 degrees Celsius in some western suburbs.
NSW Health recommended people stay indoors between 11.00am and 4.00pm.
The conditions mean firefighters are on high alert around the state today.
NSW Rural Fire Service Commissioner Shane Fitzsimmons said it would be a "very complex, very difficult day.