Pink, purple, red and gold were streaked across the sky, and soon across social media, as photos of the spectacle were posted to Facebook and Twitter.

Rob Sharpe, a meteorologist with Fairfax Media-owned Weatherzone, said the "very vivid" sunset brought "amazing colours" across the sky in much of Sydney.

"That was primarily due to the fact that we've got this low pressure trough that's now moved off the coast," Mr Sharpe said.

"So we're just seeing some high cloud off the back of that. The light is scattering beautifully through the moisture in those clouds. But also, due to the smoke that's still sitting around the Sydney area due to the hazard reduction burns."

While heavy cloud cover meant the sunset was especially picturesque in Sydney, it was also seen south to the Illawarra region, which had "blue sky and a little bit of extra colouring".

"When there's more particles in the air and particularly more moisture in the air, that leads to refraction of the light, and it's the refraction of the light into your eyes which is how you're seeing all the different colours of the sunset," Mr Sharpe said.

"We had beautiful sunsets across Sydney and the Illawarra as that cloud was starting to clear off in the wake of that low pressure trough."

On Twitter, the sunset was described as "amazing" by Sydney Airport, which posted a time lapse of planes taking off against the memorable backdrop, while others dubbed it "stunning", "incredible" and "awesome".