Thousands of people across Melbourne and Geelong remain without power after a severe storm swept across the state overnight.

Half a million lightning strikes were recorded, with one sparking a blaze at a home in Taylors Lakes.

Napoleon and Simone Trombetta's Taylors Lakes home of 35 years was hit by one of 50,000 bolts of lightning that made contact with the ground.

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The couple were in bed about 1am when their dog Frankie began to be distressed by the storm.

Moments later, the pair heard a "massive bang" before seeing a red glow from their lounge room.

"The smoke detector went off and looking from our bedroom there was a red glow, we jumped out of bed and got out there as fast as we could," Simone told 9News.

"I grabbed Frankie and my handbag and that was it."

The house has been extensively damaged from the fire, with the couple believing the fire started by a lightning strike.

It was a wild night of storms across Melbourne and Victoria more broadly, with Geelong particularly hard-hit.

The sporadic storms first hit the Mornington Peninsula, before jumping across to the Surf Coast and settling in over the city just before 11pm.

More than 900 calls for help were made over downed trees and building damage, with 200 calls to the SES in just one hour at one point.

More than 500 of those calls were in the greater Geelong area, where 80km/h winds uprooted trees and ripped roofs and brickwork off homes.

Belmont resident Dee Dove and her family were inside their Belmont home when a tree crushed their front fence.

"It was like a cyclone, I mean I've never ever experienced anything like it in all my time – it's crazy," Dove said.

"We were so lucky. There's other people around here who've lost their roofs.

"It actually makes me emotional."

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At its peak, the wild conditions left 45,000 customers without power, with a few thousand still waiting to regain electricity as of this afternoon.

The dynamic thunderstorm activity saw about 30mm of rain fall in Geelong and Lara in just 30 minutes.

Hail stones with a diameter of two to four cm also pelted the Otways and Geelong.

About 70mm fell in the Macedon Ranges overnight, but the weather system failed to quench the state's bushfire-stricken Grampians region, where just 10mm fell.

The storms followed a day of high heat, with a top of 39 degrees in Melbourne.

That high will be duplicated again today, followed by 34 degrees tomorrow.

A heatwave warning has been issued for the state.

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More thunderstorms are also expected to move across the south-west of the state this evening, with the Bureau of Meteorology predicting a risk of dry lightning.

"We're not out of the woods yet and we've had a taste of it yesterday," SES Victoria deputy chief officer David Baker said.

"We're still looking down the barrel of storm activity this afternoon and tomorrow.

"Storms can appear anywhere, at any time, but the best time to prepare is before the storm arrives."

The combination is a worry for firefighters, who are still battling two out-of-control blazes in the state's west.

Temperatures will drop to a top of 23 degrees for Melbourne on Wednesday before rising again later in the week.

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Melbourne is no longer on track to overtake Greater Sydney's population, meaning Sydney will retain its position as Australia's largest city for at least another decade.

The government's annual Population Statement had previously projected that Melbourne's population would surpass Sydney's by 2031-32, despite the sharp exodus the city experienced during the pandemic.

However, the latest statement notes that a review of overseas migration flows has changed that.

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"Having reassessed state-level overseas migration patterns, the Centre no longer projects Greater Melbourne's population to overtake Greater Sydney's by 2034–35," the statement said.

Other cities are set to experience a population boom, with Greater Brisbane projected to be home to more than half of Queensland's population from 2025–26 for the first time since 1978.

As of 2023–24, Greater Sydney's population stands at 5.6 million, making it the largest city in the country, with 66 per cent of New South Wales' total population.

However, its growth rate is expected to slow, dropping to 2.3 per cent in 2023–24 and 1.7 per cent in 2024–25.

READ MORE: Lightning strike sets house on fire as heatwave, storms grip Victoria

Meanwhile, Greater Melbourne's population is currently 5.4 million, comprising 77 per cent of Victoria's population.

Like Sydney, Melbourne's growth rate is also projected to decline, reaching 2.9 per cent in 2023–24 and 2.2 per cent in 2024–25.

Australia's population is projected to grow from 27.1 million people in March 2024 to 31.3 million people by 2034–35.

The annual population growth is forecast to decline from 2.1 per cent in 2023–24 to 1.2 per cent by 2034–35.

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The photos showed piles and piles of sodden books stacked up in mountains outside Lismore's library.

They're the images that will be forever etched in the nation's memory of the floods that ravaged the town and the NSW Northern Rivers region in 2022. 

Around 30,000 books from Lismore Library were destroyed as the floodwaters surged to 1.6 metres, reaching its collection on the second floor for the first time.

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Now, in a display of resilience and hope, Lismore's main library was reopened to customers for the first time since the floods today, as the building's extensive $5.6 million renovations near completion.

Lismore Area Librarian Michael Lewis said the finishing touches were still being put on the Lismore Library, but the council was responding to community demand to re-open the space as soon as possible.

"We know how important the library is to our community, which is why we decided to welcome them back despite the final works yet to be finalised," he said.

"With the elevator still not operational, we have temporarily relocated a selection of services from the higher levels to the ground floor."

After the floods, a pop-up Library was opened in town and a children's library operated from the Lismore Central Shopping Centre.

These temporary sites have now closed.

Lismore Mayor Steve Krieg said it was exciting to see the main building operational again.

"Like many people, I vividly remember the disturbing picture of the large pile of water-soaked books outside the library reaching up to the second story," he said.

"While we are not quite there in terms of the rebuild, the public is keen to return to their treasured library, as is the staff." 

The renovated library has been designed to be sturdier and more flood-resistant.

Federal Member for Page, Kevin Hogan, said the reopening of Lismore Library was a powerful symbol of the community's rebuild.

"Almost three years on, and today we see not just a restoration of what was lost, but a transformation that ensures this space is stronger and better prepared for the future," Hogan said.

An official opening for Lismore Library will take place in March, once the renovation work is complete.