Large parts of Australia are bracing for heavy rainfall and possible flash flooding over the coming days after an overnight deluge caused chaos in Sydney.

Emergency services received around 500 calls for assistance and performed 42 rescues after more than 100 millimetres of rain fell in under three hours in the NSW capital on Thursday night.

The deluge was particularly heavy in Sydney’s south-west, with six people helped when they were left stranded by rising floodwaters in Fairfield, and a dozen properties evacuated due to water inundating homes.

A sinkhole opened up on a busy intersection in the CBD on Friday morning, the Sydney Morning Herald reported.

A Coles delivery truck had to be rescued after its front wheels went into the hole, while a nearby school had to send students home after Sydney Water was forced to cut off the water supply.

The flash flooding also left thousands of commuters stranded on major arterial roads, including Anzac Bridge, while parts of Parramatta Road were closed.

While Sydney is expected to get a reprieve over the weekend, when thousands will converge for the annual Sydney Mardi Gras, the Bureau of Meteorology said on Friday that a severe weather warning for heavy rainfall across central Australia had now been expanded to the southern coast of southern Australia.

“Our current expectation is that this weather warning will be quite dynamic and also expand over the weekend, particularly into eastern parts of South Australia and down towards western Victoria,” said meteorologist Jonathan How.

The BOM warned that slow-moving thunderstorms would bring isolated heavy rainfall and possible flash flooding in parts of Victoria on Friday afternoon.

Central Australia could see an extra 50 to 200 millimetres of rain owe the weekend, while southern and central parts of SA are expected to receive between 20 and 150 millimetres over weekend – including up to 80 millimetres in Adelaide.

“Sunday is the key day,” BOM senior weather forecaster Angus Hine told InDaily, adding that the average March rainfall in Adelaide was 23.4 millimetres.

“There’s every chance we will get more than that over the weekend. We could even double or triple that.”

Thunderstorms are forecast in parts of Victoria, South Australia and Central Australia, and the BOM has issued a number of floodwatch warnings in both Central Australia and SA.

“So do check these before you head out, because heavy rainfall might lead to river and creek rises over the next few days,” How warned.

He added that flash flooding could also create dangerous road and travel conditions.

“A number of roads and freights and train lines are already impacted.

“For some parts of Australia, this rain will be very welcome… but that will come with its challenges.”

Several parts of Australia have been inundated in recent days, with the remote town of Birdsville in south-west Queensland receiving nearly 60 per cent of its annual rainfall in a single day after 93 millimetres of rain fell in the 24 hours to 9am Thursday.

It is expected to receive up to 25 millimetres again on Saturday and Sunday, with severe thunderstorm warnings still in place in the west of Queensland on Friday afternoon.

A wild storm also swept across Perth on Thursday morning, when a man and three teenagers were struck by lightning.

-with AAP