Parts of Victoria, including Melbourne, are in for a rough night with thunderstorms and showers expected to lash the state.
Severe thunderstorm warnings with intense rainfall, damaging, locally destructive winds and large hail are in place for western and central Victoria where wind gusts have already reached 139 kilometres per hour in Horsham.
Thousands of homes were still without power across the state, with Powercor, which supplies energy to Melbourne's west and the western parts of the state, reporting about 13,000 power outages at 10pm.
A watch and act warning was issued for western and central Victoria and parts of Melbourne on Thursday evening, with the Bureau of Meteorology urging people to take shelter.
Flash flooding is also predicted for parts of the state, including in Bendigo, Ballarat, Geelong Warrnambool and Melbourne.
Bureau of Meteorology senior forecaster Mark Anolak said there was a large area of severe thunderstorms in the west of the state.
"They are expected to continue to move eastwards towards the central districts of Victoria, including Melbourne," he said.
Wild weather is due to continue lashing Victoria, including Melbourne, over the next day or two as rainfall records fall in some parts of the state.
Thunderstorm cells tore through much of Melbourne and parts of regional Victoria overnight and on Thursday morning, leaving thousands without power.
The Bureau of Meteorology's Diane Eadie said Mildura in the state's north had recorded its wettest January day ever, with 69mm of rain recorded in two hours on Thursday morning.
She warned there was more to come, with the state's west due to be hit by fresh storms throughout the afternoon and evening.
"It's not over yet … with the risk of heavy falls continuing, with showers and storms today," she said.
"The focus of today is the west of the state, where we could see heavy falls to potentially intense rainfall rates, large hail and also the risk of damaging winds."
Ms Eadie said Thursday night and Friday, the focus would shift to central Victoria, including Melbourne.
"For the Melbourne area, the greatest risk of those thunderstorms develops from around about midday [Friday] and continues through the afternoon and evening," she said.
The weekend will bring cooler conditions, but the risk of heavy falls will remain in the state's east.
Ms Eadie said the humidity would remain, with muggy conditions due to continue until at least the middle of next week.
She said the influence of La Niña had resulted in the summer storms bringing much more moisture than those in previous seasons.
"We've seen so much moisture in the atmosphere of late, really building across much of Victoria, and as a result any storm has the potential to cause localised flash flooding and, indeed, intense rainfall rates," she said.
State Emergency Services (SES) state agency commander David Tucek warned people not to take unnecessary risks.
"Plan your trip before you travel if you do need to travel.
"If you don't need to travel, it's a good day to actually stay inside because you're going to be potentially at risk of the flash-flood risk.
"Flash-flood risk means we don't want to see people playing in floodwater, walking in floodwater, riding or driving through floodwater."
Storm cells start fires, cause flash flooding
The storms that rolled through Melbourne and parts of regional Victoria earlier brought heavy rainfall, prompting warnings of flash flooding.
And the lightning sparked hundreds of small fires across the state, with three residents from Melbourne's northern suburbs taken to hospital after their home caught alight.
The first warning for the "very dangerous thunderstorms" was issued by the Bureau of Meteorology shortly after 6am, and was cancelled just after 11:30.
The storm cells moved from areas of Gisborne and Woodend, north of Melbourne, through to suburbs in Melbourne's north and west, including Craigieburn, Footscray, Greensborough, Melton, Preston, St Albans and Sunbury.
Shortly after 8am, the weather had moved to the north-east of Melbourne, including suburbs like Greensborough and Ringwood, before hitting the outer north-eastern fringe by 9am.
"Intense rainfall that may lead to dangerous and life-threatening flash flooding is likely," the warnings read.
By about 9:30am, the Mornington Peninsula was under threat after the storms swept through the Melbourne suburb of Frankston and its surrounds.
An hour later, they had moved to Hastings and Phillip Island and were moving south-east towards Gippsland.
Rainfall approaching 'once-in-a-century' levels
Significant rainfall has already been recorded across the state, with Malmsbury in central Victoria getting 56.2mm in just one hour before 5:15am.
Arthurs Creek, about 33 kilometres north-east of Melbourne CBD, saw 41.6mm in the hour to 8:02am, and 57.8mm in the two-and-a-half hours to 8:41am.
Coldstream recorded 37.2mm in the hour to 8:46am, while Warburton recorded 45.4mm in the two hours to 9:58am.
"We've seen rainfall rates approach what we would expect to see once in a century," Jackson Browne, a senior forecaster for the bureau, told ABC News Breakfast.
Mark Analak from the bureau told ABC Radio Melbourne the city experienced "a heavy burst of intense rainfall" over a short period.
He said once the main cell moved through the metropolitan area, there would be a "fine or clear" period.
People rescued after driving through floodwaters
The SES received more than 300 calls for assistance in the 24 hours to 9:45am.
Just under half of those were in Mildura.
"What we are seeing again is tropical moisture coming down from northern Australia and that's created some significant issues the last couple of days."
Mr Gamble said the SES responded to five people trapped in their cars after driving through floodwaters in Mildura overnight, despite constant warnings to avoid driving in wet weather events.
"And the key message there is it only takes 15 centimetres of water for a small car to float."
Premier Daniel Andrews thanked SES volunteers for doing "an amazing job".
"Last night was pretty challenging and no doubt there'll be further of those challenges over the next few days with some of the forecast pretty challenging weather," he said.
Lightning causes fires
This wild weather has followed a week of hot days, with the mercury hitting more than 37 degrees Celsius in Melbourne on Wednesday, the hottest Australia Day in 16 years.
A house was struck by lightning in Bundoora, in Melbourne's northern suburbs, causing what Fire Rescue Victoria called "significant damage" to about 40 per cent of the home.
All three residents evacuated and were transported to hospital by Ambulance Victoria.
Doreen woman Lauryn Bahen said her suburb in Melbourne's north was hit with "really loud thunder, lightning and torrential rain" early this morning, partially collapsing the ceiling over her home's outdoor area.
SES crews have reinforced the ceiling, fearing larger sections could also buckle.
"They've reinforced it with wood so that more of the ceiling doesn't fall in," she said.
"You can see where it (the ceiling) has landed on a glass table. I went under it (the hole) and started pulling it out and then it started coming down and cracking over to the fan.
"I thought I would just leave it alone."
Storms hit the Wimmera region of Victoria on Wednesday afternoon, with hundreds of lightning strikes starting small fires.
Mark Gunning, assistant chief fire officer for CFA District 17, told ABC Wimmera there were 40 fires reported across the region on Wednesday, and crews were still working to extinguish some on Thursday morning.
"There would have been many more, but the rain with the lightning extinguished some," he said.
"Some crews were able to put fires out quickly, others needed machinery to assist with tree fires and the like."
"Some of the temperatures are amazing: 3000 degrees isn't uncommon for a lighting strike, and that's why things ignite even if there is rain."
