The pollution was 11-fold the hazardous levels in some parts of the city.
A user posted an aerial view of the city enveloped in smog and wrote: "The smoke enveloping Sydney is absolutely staggering. This is a crisis."
The clipping got 73.8K views, 343 retweets and 384 likes.
One Twitter user retweeted the clipping and wrote: "Let it be known that Australia is burning. Our cities have been covered in smoke in the last couple of weeks, and this is Sydney, right now. Climate change is real. Bushfires are still raging. The air isn't safe to breathe."
It had 74.1 views, with 2.5K retweets and 3.4K likes.
A concerned city dweller wrote: "We're at the point where smoke in Sydney is so bad, experts are calling for air pollution shelters".
One user commented; "This is like Kuala Lumpur in 1993 when rainforests were taken down for agriculture. This smoke is sickening!"
Another post read: "I'm saddened by the loss of nature and all the suffering animals and people have to go through because of this. Hopefully makes people think of who they vote for so the fossil coal in Australia stays in the soil (Australia is the world's largest coal exporter."
One Twitter user posted: "I'm in a city several hours away from Sydney and it's still bad enough that the horizon is obscured and asthmatics can't leave their houses without industrial rebreathers".
( With inputs from IANS )