A neighbour has described the devastating moment a well-respected community member and father of three was electrocuted by a fallen powerline in Sydney's south-west last night.

Key points: Dr Ibrahim's body could not be reached for an hour due to live wires

Dr Ibrahim's body could not be reached for an hour due to live wires A cool change saw temperatures plunge by up to 15 degrees Celsius

A cool change saw temperatures plunge by up to 15 degrees Celsius Storms left thousands without power and ripped roofs from buildings

Hossam Ibrahim, 38, died in his driveway at Acacia Avenue in Punchbowl at about 10:30pm following wild storms that had lashed the area and other parts of Sydney.

Neighbour Karen Adler said a number of residents heard a "massive, loud bang" and went outside to find electricity wires had come down.

"The guy has just come out of the house and walked into the driveway and he's pretty much walked into the wire," she said.

"We couldn't do anything.

"The boys were trying to throw things at the wire to try and get the wire off him but they couldn't touch him, they couldn't do anything.

"We knew that he was pretty much gone straight away."

At the time of the incident it had been raining only lightly and there was no lightning.

However it is understood visibility was limited due to a power outage after the earlier storm.

NSW Ambulance paramedics declared Dr Ibrahim dead at the scene.

Emergency services and electricity workers attend the scene at Punchbowl.

Ms Adler said Dr Ibrahim's family were screaming and in shock.

"[They're] a young family with three children, so we're all devastated," she said.

Neighbour 'saved' children

Dr Ibrahim's best friend, Ahmed Hegazy, praised a neighbour who he said saved Dr Ibrahim's children from electrocution.

"He was lying on the ground and his children were trying to reach him and the neighbours screamed at them [not to touch him]," Mr Hegazy said.

"One of the neighbours picked them up and moved them away so they would not be injured or killed."

Mr Hegazy and his wife went to the scene around 11:00pm last night and helped comfort Dr Ibrahim's wife, who had been taken to a neighbour's house.

He described his friend as "a good man, very kind and charitable".

"He would organise outings and camps for Muslim youth and was heavily involved in raising money for the Human Appeal and helping the Egyptian community in Australia and overseas," he said.

"Everyone liked him and his approach to people was to be kind to them."

Dr Ibrahim had studied at the University of Canberra and planned to begin another PhD this year.

In a tribute posted to social media, Mohammed Zaoud described Dr Ibrahim as an "an absolute gentleman" and one of the most polite people he had ever met.

"[He was] a quiet, humble man who worked tirelessly for the community I have travelled with him, done business with and spent years learning from him while he served as Chairman of Islamic Relief," Mr Zaoud said.

"A true loss to the Muslim community and wider Australia."

Facebook user Wassim Doureihi said Dr Ibrahim was "a kind, inspiring, principled voice in the community, with a smile always on hand, a heart always open, and a readiness to always assist".

"Many knew him, many will grieve for him," he wrote.

Delay getting to the body

Fire and Rescue NSW Superintendent Mick Henly said it took emergency workers an hour to get to the man.

The house where Dr Ibrahim died. ( ABC News: Lily Mayers )

"There was a problem in getting to the deceased person because the power lines were still live, so the electrical authorities were called and there was a delay from isolating those power lines and making them safe before the emergency responders could get in there and assist the gentlemen," he said.

A report is being prepared for the coroner.

Ausgrid said in a statement the cause of the incident had not yet been confirmed, but an investigation was underway.

"Our thoughts are with the family at this time," the statement said.

It reminded members of the public to assume that any fallen powerlines were live and to stand at least 8 metres away.

'Mini cyclone' throws roof on car yard

The roof was torn off a mechanical workshop in Smithfield, landing on a used car lot. ( Supplied: Peter Papas )

Bureau of Meteorology forecaster Rob Taggart said a very strong cold front that came through in the afternoon caused temperatures to plunge by 15 degrees Celsius.

"In weather terms it was quite exciting, with really warm and hot temperatures ahead of the change and then the change came through and a really dramatic shift in temps and at the same time quite a lot of thunderstorm activity in parts of the state," he said.

Albion Park on the south coast recorded the state's highest rainfall with 85mm, while 57mm fell at Merrylands west in Sydney's west.

Mr Taggart said the storms also featured "squally winds" and small hail in parts of Sydney.

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While the storm was not as severe as recent weather activity in Sydney, it caused significant damage in Smithfield, where the roof of a mechanical workshop tore off and landed on a used car lot next door.

Peter Papas was filling up at a service station nearby when he heard a loud bang as the roof landed on several cars.

"It was like a movie scene — it was a like a mini cyclone had hit," he said.

Mr Papas said the storm, with small hail and strong winds, had caused flowers on sale outside the petrol station to blow away.

"It was pretty intense and it all happened in a matter of 10 minutes and then it stopped," he said.

Carmel Phillip from the State Emergency Services said they had responded to 390 calls for help, most due to roof damage, leaking roofs and tree damage.

Wyong, Liverpool, Bankstown and Hornsby were among the worst-affected areas.

At the peak of the storm, 16,000 homes lost power, according to Endeavour Energy and Ausgrid.

As at 9:00am there were more than 550 homes still without power, including 430 homes in Gosford.