An emergency warning is in place for the Wye, Kennett and Cumberland Rivers in the Lorne area of Victoria's southwest coast after thunderstorms dumped more than 170mm of rain on the area, breaking river banks early on Thursday afternoon.
Local Polwarth MP Richard Riordan shared a video to social media showing at least four cars taken by a raging current at the Cumberland river caravan park.
"The Wye River, Cumberland River (and) Erskine River all in massive flash flooding this afternoon," he wrote alongside a caution for residents to take extra care.
The area is a popular tourist spot with hundreds of holiday-makers visiting at this time of year.
Caravan parks in the region are being evacuated including at Carlisle River, Cumberland River and the Lorne Foreshore.
Sections of the Wye River Big4 holiday park are also submerged in rapid floodwaters.
Susie Simonovic, who owns a holiday home in the area, described the flooding as akin to a tidal wave.
"I've seen that river burst its banks in the past, but not to this level," she told AAP.
Another resident, Kath, said the area has been inundated by heavy rain on Thursday morning before the river eventually broke its bank.
"It really was like a tsunami of water going out from the river," she told the ABC.
3AW Breakfast host Ross Stevenson called into the radio station from Lorne where he is currently holidaying.
"The main street of Lorne is now a complete traffic jam because no one can get across this bridge," he said.
"It's incredible ... I've never seen anything like it".
Dramatic footage also shared online shows at least eight cars being washed out to sea from the Wye River mouth.
The SES confirmed no injuries have been reported so far but some people remain trapped in caravans.
Wye River's Country Fire Authority captain Andrew Hack said there was little warning things would escalate.
"It came up super quick ... there was very little warning this was going to happen," Mr Hack told ABC News Radio.
"We had in excess of 20-25mm this morning and it seemed to dissipate and it looked like it was going to clear but then not long after lunch we got another huge inundation."
Alistair Drayton from the SES described the intensity of the rainfall as "significantly off-the-charts".
"The previous totals down there for a whole day total was 123mm," he said.
"In the last six hours, we've seen 178mm of rain.
"This is a significant weather event. This is significantly off-the-charts with respect to records."
The scenic Great Ocean Rd has closed in both directions from Skenes Creek Rd in Skenes Creek to Hird St in Lorne, with only emergency services allowed to pass.
The local Foodworks grocery store in Lorne was forced to shut its doors until further notice due to flash flooding, as it urged people to avoid the area.
The State Emergency Service issued a flash flood emergency warning at 2.36pm for Wye River, Kennett River, Cumberland River, Lorne and surrounds.
Residents in these areas are advised they are in danger and should move indoors immediately to shelter away from floodwater.
The Bureau of Meteorology also issued a warning at midday on Thursday for severe thunderstorms likely to produce heavy rainfall leading to flash flooding in the next several hours.
More than 175mm of rainfall was observed in the six hours to 3pm at nearby Mount Crowley.
The Lorne Community House has thrown open its doors to anyone escaping the conditions who needs shelter.
