South Australia has copped another belting with a destructive storm lashing the state just 24 hours after super cell thunderstorms knocked out the state’s entire power network.

The intense low pressure system raged across Adelaide and parts of South Australia late on Thursday. The storm packed winds of up to 140km/h, among the strongest the city has experienced, prompting an unprecedented warning from police for workers to head home early and stay home amid concerns emergency services might not be able to cope.

The winds brought down trees across a wide area, causing major damage, and ripped some mid-north buildings apart.

Heavy rain caused widespread flooding, from the Patawalonga River in Adelaide, through to the Barossa and Clare valleys, which copped 54mm of rain.

In Clare, a caravan park was under threat and in the Barossa, a dam burst, prompting an emergency flood warning for the town of Greenock.

Storm surges and huge waves also inundated some communities along the Spencer and St Vincent gulf coasts with the worst centres affected including Port Pirie, Port Broughton and Moonta.

The State Emergency Service responded to more than 660 calls for help, taking the tally to well over 1,000 in the past 36 hours.

The police commissioner, Grant Stevens, said extra police could be brought in from interstate to help cope with the crisis.

The SES chief officer, Chris Beattie, warned the service was at risk of being stretched beyond capacity.

The latest emergency came after Wednesday’s blackout when ferocious winds ripped up more than 20 transmission towers in the mid-north, taking out three of the state’s four major transmission lines.

The premier, Jay Weatherill, described the storm as “catastrophic” and said it had involved weather events not seen before in South Australia, “such as twin tornadoes, which ripped through the northern parts of our state”.

By late on Thursday, 30,000 properties remained without power, some because of Wednesday’s statewide blackout and others as a result of new damage caused by the continued wild weather.

Weatherill warned some households, particularly in northern areas, could remain without power for at least a couple of days.

At the height of the drama on Wednesday, super cell storms with destructive winds and tornadoes ripped more than 20 transmission towers in South Australia’s north out of the ground, bringing down three major transmission lines.

Lightning also damaged energy infrastructure, with 80,000 strikes hitting the state over a short period. It caused a state-wide blackout that plunged South Australia into darkness.

South Australian power transmission company ElectraNet will bring in temporary towers from interstate to repair the transmission lines.

ElectraNet executive manager of network service, Simon Emms, said the company hoped to have one of the three backbone circuits restored by Sunday and would build on that as fast as possible.

Emms said the company continued to work on restoring power to those areas of the state still without electricity but establishing a timeline was difficult.

“That’s a very fair question but very hard to answer at the moment,” he said.

“Obviously, the current wind conditions are hampering restoration efforts. Access to the sites is very difficult and we haven’t finished fully patrolling all the lines yet to ensure we can safely energise them.

“When we’ve finished the patrols, then we’ll safely energise. We’ll then restore the assets with emergency towers.”

Emms said he was not aware of any power system in the world that could handle losing as much energy so quickly without going into blackout.

He said such events were not common but were not unheard of.

Trees toppled by high winds near Melrose in South Australia. Photograph: Debbie Prosser/AFP/Getty Images

Meanwhile, parts of New South Wales were being hit by the tail of the storm cell as it moved on from South Australia.

The weather bureau had warnings in place for damaging winds and potential flash flooding for much of the state, but had revised down warnings for heavy rains.

Broken Hill has borne the brunt of the destructive winds, with gusts reaching up to 90km/h.

Thunderstorms were hitting towns in the north of the state along the Queensland border.

The Riverina, central and south tablelands and parts of the Hunter, Snowy Mountains and mid-north coastal regions were all on alert.

Towns in flood-ravaged central NSW were also being told to prepare for potential flash flooding and further flooding in the next few days.

The central west community of Forbes could be inundated by a second peak of the Lachlan River at the same time the town’s weekend floodwaters reach downstream Condobolin.

The SES predicts the high water marks would occur sometime next week, with 30mm of rain expected on Thursday and up to 20mm on Friday.

At least 50,000 sandbags had been transported into the towns from Maitland in the Hunter Valley and extra crews brought in from around the state.

About 100 properties remained subject to an evacuation order while sittings at courthouses in Forbes, Condobolin and Lake Cargelligo had been cancelled for next week.

The SES was calling on those going to the Deni Ute Muster or travelling inland to check for potential road closures.