Sydney, Melbourne weather warning issued with huge storm about to strike

Australians in the country's southeast are on high alert amid a supercell storm that has already brought golf ball-sized hail, flash floods and torrential rain.

The storm system has been wreaking havoc across central and northwestern Victoria, with the state hit by heavy rain and large hail on Wednesday and Thursday.

Meteorologists have warned more destructive weather is in store for Friday, with Sydney , Melbourne , Canberra and Hobart all expected to be hammered by rain, thunderstorms and damaging winds.

The Bureau of Meteorology said Aussies in the southeast can expect 'another big storm day' on Friday, with Sydney to cop as much as 15mm of rain.

Melbourne and Canberra are both forecast to receive between 10mm to 35mm, while Hobart could see up to 25mm of rain today.

Severe thunderstorms are also possible in central and northeastern parts of Victoria.

'Anywhere that thunderstorms form, there is that potential for flash flooding underneath due to that heavy rainfall,' BOM meteorologist Sarah Scully said.

A severe weather warning is currently in place for parts of Victoria's Central, East Gippsland, North Central, North East and West and South Gippsland regions.

'A deep low pressure system will cross southern Victoria and Bass Strait during Friday,' the BOM said.

'Strong winds averaging 50km/h to 60km/h with damaging wind gusts of around 90km/h are expected about the central and northeastern ranges, with the risk extending to the outer northern suburbs of Melbourne from mid morning to around midday on Friday.'

In NSW, strong wind warnings are in place for the Byron Coast, Coffs Coast, Macquarie Coast, Hunter Coast, Sydney Coast, Illawarra Coast, Batemans Coast and Eden Coast.

Ms Scully said the wild weather is set to ease by Saturday morning.

It comes after the rural town of Casterton, 350km west of Melbourne, was devastated by apocalyptic weather on Wednesday afternoon.

The streets were left covered by a thick blanket of large hailstones, while heavy rain saw flash flooding on main roads.

Some businesses were forced to temporarily close after they became flooded, with windows smashed, roofs caved in and cars completely destroyed.

The local State Emergency Service and Country Fire Authority received nearly 100 calls for help from the town that has a population of about 2,000.

Despite the wild weather, Sydney will see a warmer day on Friday with a forecast top of 26C.

Melbourne is looking at a maximum temperature of 24C, while Adelaide will see a sunny day with a high of 20C.

Hobart has a maximum temperature of 18C for Friday, while Canberra will enjoy a balmy 21C/

Brisbane will meanwhile see a warm weekend with temperatures to linger around the high 20s and low 30s.

Darwin will get as hot as 33C on Friday and Perth is to see a weekend in the low 20s.