More than 55,000 properties in Sydney and the Central Coast remain without power after thunderstorms savaged the New South Wales east coast.
Torrential rain, damaging wind and hailstones the size of golf balls lashed Sydney and the Hunter region on Saturday afternoon, bringing down trees and taking out hundreds of power lines.
Sydney's north was hardest hit with areas of the Campbelltown area and the southern part of the Central Coast also damaged.
Network operators Endeavour Energy and Ausgrid said more than 750 electrical hazards needed to be repaired before supply could be restored to 56,000 homes.
"This was a devastating storm that caused extensive damage to the electricity network," Endeavour Energy spokesman Peter Payne said on Sunday in a statement.
"Many of our customers in the worst affected areas would not have seen damage like this for years."
Ausgrid's Jonathan Hall said repairs could take a while.
"Unfortunately, it's taking time because that does involve in some places putting in new power poles and new power lines and unfortunately that type of repair takes some time."
Lightning struck a train line at Granville, bringing services to the city's west to a halt for hours.
Emergency crews worked through the night to restore power and clear debris and the operation is expected to continue into Sunday morning.
Sunday's weather is expected to remain overcast with a high chance of further showers.
Further south, flash floods caused havoc for some in Melbourne on Saturday afternoon, with flash flooding turning backyards, suburban streets and ponds into gushing rivers.
A Christmas party at a Pakenham housing estate in the city's outer southeast was called off Saturday afternoon when heavy rainfall halted celebrations.
Organiser Samantha Thorpe said a little pond nearby became "like a raging river".
"It has never happened like this before."
Just as amazingly, Ms Thorpe said, within an hour of the deluge, the water had drained away and the sun was shining, as if it hadn't happened.
A general severe thunderstorm warning remains in place for most of the state.
Thunderstorms lashing parts of Victoria have seen up to 13mm of rain fall every five minutes in the early hours of Saturday and a severe weather warning is also in place for parts of Victoria including Shepparton, Seymour, Castlemaine, Kyneton, Ballarat and Wangaratta.
Emergency Management Commissioner Andrew Crisp said the bad weather had been widespread.
"There weren't too many parts of the state that have been spared the impact of the weather event we've seen over the past 48 hours," he said on Saturday.
Bureau of Meteorology's Kevin Parkyn said intense storms and heavy rain were expected to continue in Melbourne on Saturday afternoon and night.
He said the relatively rare weather conditions could bring flash flooding too.
In the 24 hours from 7am on Friday the SES received 693 requests for assistance across the state, with 123 of those calls from the Malvern area.
Most calls were about flooding or building damage.
Other areas badly affected included Bacchus Marsh, Port Phillip, Wyndham and Hobsons Bay.
Tasmania has also been hit by heavy rain, causing flash flooding.
A severe weather warning for heavy rain remains in place for some parts of the state, and rainfall up to 80mm is expected.
Meanwhile, the cyclone system moving over northern Queensland has been downgraded to a tropical low but there is a chance it could reform off the state's east coast.
Cyclone Owen weakened as it passed near the Gulf of Carpentaria and was downgraded on Saturday afternoon.
Despite the warning level reduction, Owen still has sustained winds of 65kmh at its centre and gusts up to 85kmh, along with thunderstorm activity and heavy rain.
Flash flooding is expected to remain a threat and residents of the state's north are being urged to follow emergency advice.
