For Jason Paterson and Michael Bath, the dramatic tornado that hit the skies above the small Northern Tablelands village of Ben Lomond on Saturday afternoon was a once in a lifetime weather event.

The tornado, which the men filmed from nearby Glencoe, dropped from beneath a rapidly rotating wall cloud shortly after 4pm.

The sighting came as the Bureau of Meteorology warned severe thunderstorms could produce more tornadoes, destructive winds, large hail stones and heavy rains which could lead to flash flooding in the region.

Areas set to be affected included Tenterfield, Inverell, Armidale, Glen Innes, Tamworth and Moree.

Mr Paterson said he had seen similar tornadoes during trips to Texas, Kansas and Nebraska in the United States, but never in Australia.

‘‘It’s very rare,’’ he said.

‘‘A certain set of weather ingredients have to happen for it to happen, including wind shear, cloud height, instability. The conditions need to be very unstable for this to happen.

‘‘In Australia these ingredients only come together once in a blue moon.’’

‘‘That’s why there is a misconception they don’t happen here, but they're certainly out there you just don’t see them ‘‘putting down a tube’’, as we call it, very often.’’

‘‘It was amazing. Thrilling, actually.’’

Mr Paterson said only a handful of storm chasers had seen a tornado on Australian shores.

The wild winds which helped form the tornado tore the roof off a house in Tenterden, not far from Guyra.

The elderly woman who lived in the Tenterden Road property escaped the destruction and was lucky to be alive, a NSW State Emergency Services spokesman said.

‘‘From all accounts she’s escaped unharmed, miraculously, and she’s been taken away somewhere safe to be looked after,’’ the spokesman said.

‘‘Because it struck in such an isolated area we don’t think any other homes were affected.

‘‘Where the tornado formed and struck was pretty much on her property.’’

‘‘It’s not as if it tracked out to the coast and left a path of destruction. It came and went pretty quick.’’

A NSW Rural Fire Service spokesman confirmed heavy rains and strong, gusty winds had caused some damage to properties in the region.

''It ranged from quite severe damage like the house which lost its roof but also to minor damage,’’ he said.

The spokesman said emergency crews were working to protect damaged homes from water damage should more rain fall overnight.

Emergency services crews were called out to homes in Moree, Inverell, Armidale and Tamworth to remedy fallen trees and leaking and damaged roofs.

The SES spokesman said they had been told to expect volatile weather conditions during the next couple of days.

‘‘These storm cells are forming out of nowhere, moving really quickly, dumping these very heavy rains and then they’re gone,’’ he said.

‘‘Just when we think they’ve gone and we can rest they pop up again.

‘‘They’re very unpredictable.’’

The bureau also issued a severe weather warning for parts of Sydney, including Penrith, Parramatta and Campbelltown, as well as the Illawarra, Hunter and central tablelands on Saturday night.

Thunderstorms were expected to bring large hail stones, heavy rainfall that could lead to flash flooding and damaging winds.

A string of fierce storms have left a trail of destruction throughout coastal NSW in recent days.

Thunderstorms wreaked havoc on Sydney’s train system, and at Sydney Airport, on Friday night, causing long delays for commuters.