Authorities have defended the timing of warnings for holidaymakers along Victoria’s surf coast who were hit by an “unprecedented” downpour on Thursday, as flash-flooding warnings are now being issued for the NSW south coast.

Cars were washed into the ocean and campgrounds flooded at Wye River on the coast on Thursday, after the region received 180mm of rain causing flash-flooding of the Wye, Kennett and Cumberland rivers.

About 400 people, including those staying in the caravan park, were displaced, and dozens of vehicles were destroyed.

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Colac mayor Jason Schram criticised the level of warnings given to holidaymakers, saying: “The big question I’ve got to those in charge is, how could they not predict 180 [millimetres] of rainfall in that catchment?”

“It’s pretty messy, with mud, debris and, of course, everyone’s personal belongings, caravans, camping gear,” he told Guardian Australia.

People collect their belongings from a caravan park after flash flooding washed them away. Photograph: Michael Currie/AAP

Dharni Giri, spokesperson for Victoria’s emergency management authority, the State Control Centre, said the Wye River and Lorne were hit by “an unprecedented weather event”.

“We got over 180 millimetres of rain in just a six-hour period. Because of the terrain where the rain fell, it accelerates the water flows down through the river systems coming off of Mount Kelly,” she said.

It is the highest rainfall ever recorded in one day at Lorne, with the previous record being 123.2mm on 30 September 2021.

Giri said more than 10,000 people in the area received a text alert telling them to go to higher ground, “so, in our eyes, warnings were not issued late”.

“It was an unprecedented weather event, and our response was pretty incredible when you think about how quickly it happened and how quickly we were able to mobilise SES crews, the local CF brigade, and other emergency partners,” she said.

“Thank God, we haven’t had any deaths or injuries as a result of what happened yesterday, and it’s probably because of the quick action that emergency services took when we did get reports of that flooding.”

A spokesperson for the Bureau of Meteorology said it monitored conditions and observations closely throughout the day, and issued severe weather warnings after 45mm of rain was recorded in one hour at Mount Cowley, in the Otway ranges near Lorne.

The clean up along the Victorian surf coast begins. Photograph: Michael Currie/AAP

“A severe thunderstorm warning for heavy rainfall that may lead to flash flooding was issued at 11:57am AEDT,” the spokesperson said. “This warning was soon escalated to include intense rainfall with the risk of flash flooding over the Surf Coast as the rainfall observations continued to climb rapidly at Mt Cowley.

“This warning also prompted the SES to issue their own Watch and Act warning for the area.”

Senior meteorologist at the Australian Bureau of Meteorology, Angus Hines, said there would be more flash flooding across the southern parts of NSW and Victoria in coming days.

“There is a severe weather warning for Friday,” Hines said. “We can see it extends from Wollongong down to the Victorian border, covering the South Coast area and parts of the Illawarra in this region.

The floods carried tents, camping equipment and campers’ personal possessions on to the beach and into the sea. Photograph: Michael Currie/EPA

“We’ll likely see some damaging wind gusts on Friday, up to about 100km an hour. We will also see some heavy, persistent rain.”

The Illawarra and south coast of NSW could receive between 150 and 200mm of rain between Thursday afternoon and Saturday night, Hines said, with “significant” flash flooding.

“Where heavy rain occurs, either with thunderstorms or in the severe weather warning area, there’s likely to be disruption and delays to travel and transport, including road closures,” he said. “It’s going to be very rough on the coastline for boats and maybe even have an impact on flights and travel.”

Flash flooding was so strong it washed cars into the sea. Photograph: Michael Currie/AAP

Severe winds are expected to make it difficult to fight the bushfires in Victoria, with seven large blazes still burning across the state as of 1pm Friday, Giri said – although none were at emergency warning level.

“More than 411,000 hectares (1m acres) of land have been burnt as a result of these fires,” Giri said. “And a state of disaster remains in place until the eighth of February.”

Hundreds of stranded holidaymakers were evacuated from flooded campgrounds. Photograph: Michael Currie/AAP

She said the rain had brought cooler conditions, which had helped contain the Ravenswood/Harcourt and Wyperfeld national park fires. But authorities have asked communities in affected areas to remain vigilant because more hot weather is on the way for Victoria next week.

“We aren’t expecting the catastrophic fire conditions that we had last Friday or about a week ago,” she said. “But that being said, it’s definitely fire season and it’s definitely high-risk weather season, so we are asking communities, especially those in the impacted areas already, to just remain vigilant.”

The climate crisis is making the country more vulnerable to extreme and unpredictable weather and natural disasters, a report from the Insurance Council of Australia warned in October. This week, the World Meteorological Organisation (WMO) said 2025 had continued a three-year streak of “extraordinary global temperatures” during which surface air temperatures averaged 1.48C above preindustrial levels.