(CNN) More than 50 people were treated for asthma and breathing-related problems in Sydney on Tuesday as smoke blown from New South Wales bushfires engulfed the Australian city in thick smoke.

Air quality dropped to "hazardous" levels in the Sydney area overnight, according to the New South Wales Bureau of Meteorology.

In some areas of Sydney, the air quality was so bad that officials warned everyone to "avoid outdoor exertion and stay inside as much as possible."

Children, older adults and people with heart and lung conditions are the ones most likely to suffer from air pollution and excessive smoke, the NSW health department warned.

A spokeswoman for the NSW Ambulance told CNN that from 6 a.m. to 4 p.m. on Tuesday, more than 52 people were treated for asthma and breathing-related incidents.

#Smoke haze over #Sydney looking east over Rushcutters Bay pic.twitter.com/8XqPxYYExd — Prof Kerryn Phelps AM (@drkerrynphelps) November 18, 2019

"With high levels of smoke around today, it is important that anyone with respiratory issues takes extra care. Even healthy adults and children can be impacted by the effects of heavy smoke which can result in lung irritation," warned the NSW Ambulance service in a Facebook post. "If you have a pre-existing medical condition make sure you have all your medications with you and readily available at all times."

'I'm having trouble breathing'

Sameer Badar took a video of the haze in Avalon Beach, north of Sydney, on his way to work.

"The smoke is settling in the atmosphere and is getting quite thick, as an asthmatic I am having trouble breathing due to the dense air," he told CNN. "I can smell it quite clearly, today was a 38-degree day and the whole day the city was covered in haze due to the smoke."

"I believe the smoke is much more prominent and is affecting me and others a lot more in recent days. Before today, there was less smoke but the sky was colored a red/orange color."

Adele Bryant, who lives close to Rouse Hill in Sydney, shot a time-lapse video of her smoky commute.

She told CNN she woke up at 2 a.m. to check her house because it smelled like it was on fire.

"We are still a long way from the fires but it's definitely affecting us," Bryant said. "The smoke smells incredibly strong today."

"I was up checking all our windows and doors were shut because it smelt like our house was on fire. A lot of my colleagues are complaining that it burns their eyes being in it and a lot of issues with asthma in our office."

Schools closed in South Australia

At 9 p.m. on Tuesday, more than 1,800 firefighters were still battling 55 bush and grass fires burning across NSW, with 25 yet to be contained, according to the NSW Rural Fire Service (RFS).

The NSW RFS tweeted Tuesday that crews were battling fires in hot and windy conditions to contain 6,000km (3,728 miles) of fire edge -- "the equivalent of flying from Sydney to Perth... and back again."

NSW RFS warned that "some of these fires are expected to join in coming days."

Very smoky conditions are continuing across many areas today. The smoke is likely to hang around for the next few days. If you're easily affected by smoke, take steps such as staying indoors, avoiding exercise and taking reliever medicine if you need to. #nswrfs #nswfires pic.twitter.com/9uYC8CsQx6 — NSW RFS (@NSWRFS) November 18, 2019

In the state of South Australia, the Department of Education announced more than 100 schools would be closed Wednesday as a "Catastrophic Fire Warning" was forecast in seven districts in a tweet by the state's Bureau of Meteorology.

Paul Lainio, meteorologist with the South Australia Bureau of Meteorology told media Tuesday that temperature records were expected to be broken in the state Wednesday and there could be gale force winds as well making the situation worse.

"People should take care (and) should make preparations for possibly very dangerous conditions," Lainio said.