At least 100 stores located inside Westfield Hornsby Mall remain closed on Tuesday as authorities continued to assess the damages inflicted by a mini tornado that ripped Australia's Central Business District on Monday afternoon.

Among those that remain closed were Lowes and Oporto eatery.

"When it's safe to do so we will look at re opening as quickly as we can," The Australian quoted an unidentified Westfield spokeswoman.

Jason Carter, a Lowes staff, said water leaked into the store through the roof on Monday as as aftermath of the freak mini tornado.

"We ended up with a bit of a waterfall in the back corner but we don't know the damage because they evacuated us," he said.

"We are waiting for the (Lowes) area manager - he's on his way - just to see what he says."

On Monday at 3pm local time, a severe storm cell hit the Hornsby suburb, toppling down trees, crushing cars and ripping off roofs from establishments. It also closed roads and suspended train line operations.

BREAKING: Picture sent in from @2GB873 listener of demountable building blown off its foundation at #Hornsby.

— Sydney Live (@SydneyLive2GB) November 18, 2013

The fourth tornado to touch down NSW in 2013, weather experts have yet to determine its size.

"With tornados, we're used to seeing the American TV version where they destroy everything in their path," Andrew Treloar from Weather Services for NSW Bureau of Meteorology said.

"They range in size from about 10m to 1km at the base and without being there it's hard to know exactly how big this one was."

"It was certainly a significant system, capable of causing major damage and injury, but it won't be ranking up there with the higher end systems from the United States."

Sean Carson from the Bureau of Meteorology estimated the tornado may have had wind gusts that were in excess of 100 kilometres per hour.

PHOTOS: Amazing pic shows just how close one driver came to well lets not go there

— Triple M Sydney (@TripleMSydney) November 19, 2013

"This system near Hornsby was obviously pretty short lived. It probably didn't have enough time to pick up all that debris and make it classically seen as a tornado," he said.

A witness told ABC News she saw part of the roof of the cinema inside the Westfield shopping centre tore off.

"Debris sort of going up in a spiral into the sky so it looked like a mini tornado," she said. "There was this noise like a roar almost and we sort of all stood still," she said.