By Adrian Black

Thousands of residents in NSW, Victoria and SA are without power as powerful storms make their way across the country.

A large cold front colliding with a warm and humid airstream coming from the north is delivering prime conditions for wild storms.

Severe weather, hail and flash flooding hit parts of SA overnight, with wind gusts of more than 130km/h recorded at Port Pirie and Roxby Downs, and a 36mm deluge in one hour reported at Mount Horrocks.

While things have begun clearing in and around Adelaide, more than 5500 South Australians were still without power on Friday morning, down from around 20,000 overnight, as the wild weather continued eastward.

“The risk of thunderstorms will be widespread in the east, from southern Queensland through NSW, Victoria and into northern Tasmania.” senior Bureau of Meteorology forecaster Miriam Bradbury said in an update.

There was also a risk of storms in parts of inland Queensland and the NT, but these were unlikely to bring much rainfall, she said.

Severe storms were most likely across NSW’s central and southwest slopes, and in northeast Victoria, potentially bringing giant hail and damaging winds in excess of 125km/h.

“These storm hazards may lead to downed trees or branches, power outages, dangerous driving conditions with water or debris over roads, localised flash flooding and some property damage due to winds,” Ms Bradbury said.

In SA, structural damage to high voltage transmission lines have cut power to BHP’s Olympic Dam mine and parts of Roxby Downs.

“ElectraNet crews are working to restore power as soon as possible, and we are working with them to better understand the scale of the impact and recovery timelines,” a BHP spokesman said.

“In the interim, back-up generation and business continuity plans are in place.”

In western NSW, extensive damage to transmission towers during recent storms left more than 1400 residents without power in and around Willcannia, while backup generators were powering customers in nearby Broken Hill.

More than 3000 Victorians were without power on Friday morning.

Casterton, in Victoria’s west, was struck on Wednesday afternoon by what some locals called the worst storm they had encountered.

“Everyone is in shock by the sheer ferocity of it,” Heidi Herbert from Herbert’s Bakery said.

“I’ve never heard a noise like it before. It was like a freight train but worse.”

The bureau said Casterton copped a 20 to 25 minute bucketing which included strong winds, 5cm hail and flash flooding.

“There was heavy rainfall of about 22 millimetres in 20 minutes… that doesn’t sound like heaps of rain but when it falls in 20 minutes that’s significant,” Ms Bradbury said.

Victoria’s State Emergency Service took more than 100 calls, with at least 70 relating to building damage or flooding.

Flood watch warnings could be issued in the coming days, but the front itself is expected to drag the severe weather offshore by Saturday afternoon.

“Southern Victoria, Tasmania and eastern NSW will see easing showers during Saturday, with gusty southerly winds,” Ms Bradbury said.

Crowds heading to the MotoGP at Phillip Island, southeast of Melbourne, have been told to reconsider travel plans.

“Try and hunker down, make sure you’re where you need to be by (Friday) morning or put your plans off through those high risk areas,” Victorian SES commander David Baker said.

There’s also an increased risk of thunderstorm asthma for northern parts of Victoria.

The wild weather is expected to ease in eastern and southeastern Australia by Sunday,  for a mostly dry and relatively sunny close to the weekend.