Severe weather warnings have been issued as yet another low pressure system hits Australia’s east coast, just two weeks after it was ravaged by storms that brought wild winds, king tides and floods.

A system is expected to form off NSW’s Illawarra coast this evening, leading to heavy rain, possible flash flooding and damaging winds of up to 90km/h in the Illawarra-South Coast area, before moving south overnight.

Twenty-four hour rainfall totals are expected to exceed 150mm in some parts.

Construction crews meanwhile have continued work to fortify a giant sand wall in Sydney’s northern beaches region, in a bid to prevent rough surf from damaging the beachfront.

Erosion has already affected Sydney’s Collaroy, Dee Why, Freshwater, Narrabeen, Shelly Headland beaches, with multiple properties in Collaroy left on the verge of sliding into the sea after earlier storms.

While no king tides are expected, it is feared wild weather might further destabilise already damaged homes.

Sydney’s south-west saw flooding today, with the Georges River overflowing after more than 20mm of rain fell within seven hours.

A flood watch has been issued for the Nepean and Hawkesbury rivers.

A new low pressure system is descending on Australia's east coast. (Weatherzone)

The Bureau of Meteorology has also warned dangerous thunderstorms will affect the Brisbane and Strathpine regions of Queensland. More heavy rainfall is anticipated tonight, as well as the possibility of flash flooding.

Widespread rainfall totals are expected to reach somewhere between 50 and 80mm, with isolated falls in excess of 100mm “possible”.

The Brisbane suburb of Kenmore has already recorded rainfall of 68mm, while Greenhill has recorded 65mm in just one hour.

Residents of low-lying properties in areas such as Morayfield have taken to laying sand bags as a precaution against flooding.

Widespread rainfall across northern NSW and southern Queensland. (BoM)

Isolated flooding has already been reported in a number of areas, including Toowoomba and the Sunshine Coast.

A flood watch has been issued for the Georgina and Diamantina rivers, and the Cooper Creek, Bulloo, Paroo, Warrego, Balonne, Moonie and Border rivers.

Weather experts have assured the public nevertheless the low will be nowhere near as fierce as early June’s “Stormageddon”.

NSW SES Deputy Commissioner Mark Morrow said the front was generating slower than expected but urged people to keep up to date with warnings.

Parts of Queensland's outback have already seen heavy rain, with falls of up to 100mm have been recorded around the Queensland town of Charleville since 9am yesterday.

Former Mt Isa mayor Tony McGrady says the rain has put a smile on the faces of locals, and forced the cancellation of the Mt Isa show.

"We've had good rain but it hasn't been sufficient to make the rivers flow," he told ABC radio.

"[But] people are going around smiling."