Mini tornado tears through Dubbo as severe storms hit NSW

Hail and heavy rain have pelted parts of Sydney as storms sweep across NSW.

A reported tornado has swept through Dubbo and damaged several homes, while hailstones the size of 20 cent coins have pummelled parts of Sydney.

At least four people have been rescued from floods, including a woman pulled from a vehicle in Rouse Hill in Sydney's northwest, SES spokesman Phil Campbell says.

"These storms are bringing hail and reports of some flash flooding down near Wagga Wagga," he said.

One woman posted a Twitter photo of hailstones beside a 20 cent coin as other pictures of hail blanketing backyards emerged on Monday night.

Sydney and the Illawarra region have been worst hit, but more than 100 calls to the SES have been scattered across the state, Mr Campbell says.

The Bureau of Meteorology has issued a flood watch warning for the region, along with the South Coast, Lachlan and Nepean River Valleys.

Rainfall totals in the range of 100-200mm are expected on Monday night and Tuesday, with higher localised falls of over 300mm possible, according to the BOM.

"Heavy rain and the potential for flash flooding (are) the main threats," BOM regional director Stephen Lellyett said

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A Tornado has torn through Dubbo in Central NSW, causing damage to at least three houses.

The unusual weather event occurred about 5pm EST.

The strong winds caused trees and fences to fall and there's reports of missing property including three boats.

EARLIER: Brace yourself Sydney, the rains are here.

The Bureau of Meteorology has issued a severe thunderstorm warning for parts of New South Wales with an unstable weather system bearing down on the state.

While the CBD should be spared the worst of the storms, city-dwellers can still expect heavy rainfall in coming days.

Sydney has recorded only eight millimetres of rain so far this month, but the bureau says it could close in on it's August average this week, with up to 80 millimetres of rain expected.

A severe thunderstorm warning remains in place for Newcastle, Cessnock, Maitland, Orange, Bathurst and Katoomba.

Residents can expect large hailstones, damaging winds and heavy rainfall that could lead to flash flooding.

The wild weather is expected to worsen tomorrow and Wednesday, as a low-pressure system forms off the NSW coast.

News break - August 24