The storms also battered neighbouring Queensland, where a 22-year-old man was electrocuted in the state capital Brisbane, after touching a felled power line.
It was the third major storm in the region in just 10 days, after severe weather battered the capital Sydney and the town of Dubbo, leaving two dead. Authorities have warned more are on their way.
The town of Casino bore the brunt of Wednesday night's storm, which ripped roofs from houses, brought down brick walls and shattered thousands of windows.
"The roofs were peeling off buildings, flying up into the air and colliding with other roofs," motel operator Barry Reynolds said.
"I had guests staying here telling me they crawled into the cupboards because you didn't know what was going to happen."
Electrocuted
One 80-year-old woman was rushed to hospital with a severed artery caused by flying glass.
The storms also battered neighbouring Queensland, where a 22-year-old man was electrocuted in the state capital Brisbane, after touching a felled power line.
Reports say the bill for all three storms has reached an estimated 80m Australian dollars (US$45m).
Officials in Casino expect the clean-up operation will likely take several days.
Local member of parliament Thomas George said he had never seen anything like it in his 52 years in the town.
"I've lived here all my life, and I've never witnessed a storm like [this]. We had hailstones the size of cricket balls," he said.
Sydney
The effects of the weather were felt as far south as Sydney, with even the famed Bondi Beach experiencing flooding.
The city is still recovering from the battering it took on Monday night when it was hit by a freak storm which brought winds of 110kph.
An eight-year-old boy died when fencing was blown over and tens of thousands of homes were left without power.