A couple of locations experienced flash flooding.
Strong winds also hit parts of central New South Wales, whipping up huge dust storms which blanketed entire towns.
With gusts clocked at over 100 km per hour in some parts, dramatic vision uploaded to social media showed sections of roof from the Bringelly Village Shopping Centre in Sydney's west flying through the air and smashing into traffic on a main road. There they call it a Haboob dust storm, "he said".
"Fortunately, I rode my bike today", Hilary Wardhaugh said on Twitter and posted a video of a parking lot in the National Library of Australia where the rear windows of the cars had been smashed by the hail.
"It was like Armageddon, basically", she recalled.
As Australia takes stock of what it lost in the epic fires, some forests and other important habitats might not be able to recover fully, particularly if more droughts and fires return, as the Associated Press reports. "Incredible. People ran into the library, but I really hope nobody gets caught".
The storm damaged 65 glasshouses and wiped out years of research.
This handout photo taken on January 17, 2020 and received on January 20 courtesy of Marcia Macmillan shows a dust storm in Mullengudgery in New South Wales.
"Day turns into night!"
The National Museum of Australia also shut its doors after the storm tore external roofing, damaged shade cloths and caused leaks in corridors, the cafe and galleries.
Weather officials are urging people in New South Wales to brace for more unsafe winds, large hailstones and heavy rainfall.
It's an epic case of weather whiplash, and while these rains are helping firefighters gain control of some of the fires and even extinguish many of them, they're not going to end the drought or remove the bush-fire danger entirely during the rest of the summer there.
The fires have claimed at least 28 lives since September, destroyed more than 2,600 homes and razed more than 10.4 million hectares.
New South Wales was hit by heavy rains while Narromine and nearby communities saw very little rainfall.
Much-needed rain is continuing to fall on parched NSW farms and fire grounds with thunderstorms expected to hit the state's south over the coming hours.
Officials have warned that the effect of the fires, which have already burned for months, will be crippling for farmers, with the livestock toll exceeding 100,000 across Australia and the future hard to predict.
"Ultimately, we need to remain vigilant", Andrews said, adding the fire season, "is far from over".