Victorian authorities have told thousands of visitors and residents in East Gippsland – an area half the size of Belgium – to leave immediately as a bushfire threat looms.

The emergency management commissioner, Andrew Crisp, issued the order on Sunday ahead of what the Bureau of Meteorology has called one of the “significant fire weather days in Victoria’s history”.

The final two days of the Falls Festival in Lorne, south-west of Melbourne, were cancelled on Sunday morning in anticipation of the extreme fire risk.

Everyone in East Gippsland must leave the area today due to the fire danger forecast for tomorrow. Do not travel to this area. It is not possible to provide support and aid to all the visitors currently in the East Gippsland region.



Full info here: https://t.co/IlcPMgnLJ7 pic.twitter.com/XJBwFdGVej — CFA Updates (@CFA_Updates) December 29, 2019

The Otways in south-west Victoria, where the festival is held, and the alpine region including east Gippsland, are forecast to experience extreme heat and damaging winds, and thunderstorms are expected to bring dry lightning and new bushfires on Monday night.

There were three active fires in east Gippsland on Sunday with a combined area of more than 130,000ha. An evacuation warning has been issued for the east Gippsland town of Goonergah, which is surrounded by high-value old growth forests.

East Gippsland is popular with campers and holidaymakers over the New Year period. Up to 30,000 people are on holiday at Lakes Entrance, 300km east of Melbourne.

The main road in and out, the Princes Highway, was likely to be affected by fires on Monday, Crisp said. The Great Alpine Road, the other road out of East Gippsland, is already closed due to bushfires.

“What we are saying now, based on the conditions that will be confronting us tomorrow across the state, but in particular in east Gippsland, is that if you’re holidaying in that part of the state, it’s time that you left,” he said.

“We want to give people time to leave east Gippsland now. So if you’re camping, if you’re in a holiday home, it is time … to leave this afternoon.”

Emergency Victoria outlined a potential impact zone beginning just east of Bairnsdale and extending south along the coast to Cann River and then north to the NSW border. North of Bairnsdale, the impact zone stretches up to Omeo and then cuts back to the Deddick Valley.

The total affected area is about 15,000 square kilometres.

People who live in east Gippsland have been advised to stay with family or friends in Bairnsdale or other larger towns, and to leave no later than Monday morning.

Crisp said Parks Victoria was considering closing national parks in the region and warned that camping in a national park was “the last place you should be”.

“We are giving you fair warning: you should not be in the parks,” he said. “You might think you know where the fires are. There could be fires that start and they could be close to you. You might not find a way out of where you are at the moment.”

Crisp said 550 state forest firefighters and 300 Country Fire Authority volunteers were standing by as well as 70 helicopters and water-bombing aircraft, but “there isn’t enough trucks to go around”.

“So don’t count on a fire truck protecting your particular house,” he said. “You need to get out of there.”

Crisp advised people to register with the Red Cross’s unification service as they left to help emergency services trying to locate missing people and to reassure their families.

The fire danger is forecast to be extreme in seven of the nine districts of Victoria, and severe in the remaining two, which includes east Gippsland.

Kevin Parkin, a senior meteorologist with the bureau, said Monday was “likely to be one of the significant fire weather days in Victoria’s history”.

Parkin said temperatures were forecast to top 40C across most of the state, including Melbourne and parts of East Gippsland, but the dangerous fire conditions were due to a wind change that would reach the south-west coast between 1pm and 2pm, and would reach the Gippsland fire grounds near midnight on Monday.

“The wind change is very problematic when it comes to fires and the landscape because it lights up the whole flanks of fires quickly,” he said. “It’s a very serious life-threatening situation. Make no mistake about it.”

South Australia also faces a potentially catastrophic day on Monday in three districts, including the Adelaide Hills, where a large blaze continues to smoulder.

Authorities fear a possible repeat of the devastating blaze 10 days ago that burnt through 25,000 hectares and destroyed more than 80 homes, with high temperatures and strong winds forecast.

Country Fire Service chief officer Mark Jones said it was regrettable that the same conditions had returned so soon.

“Particularly when firefighters have been labouring for five days already before Christmas and for five days since Christmas in the field addressing the fire and tackling hotspots to black them out,” he said.

“The potential for hot-spot breakouts tomorrow is incredible across the whole fire zone.”

Catastrophic conditions will stretch across the Adelaide Hills, through the mid-north and across to Yorke Peninsula.

Other areas of the state will have either extreme or severe warnings in place, prompting the CFS to call in extra firefighting aircraft from Victoria.

The worst of the conditions will occur on Monday morning, which Jones said was unusual and meant people considering leaving should be ready to make the call early.

Temperatures are forecast to reach 40C in Adelaide ahead of a cool change just after midday. That change that will bring the worst of the conditions, with wind speeds to rise to about 40km/h.

Jones said Monday’s forecast winds most likely risked fire breakouts along the southern flank in the Adelaide Hills fire zone, but shifting conditions meant that the whole fire perimeter could be at risk at different times.

In New South Wales the worst fire danger will come on Tuesday when the wind change will move up the coast. The entire coastal stretch of NSW up to the greater Sydney region, then moving inland to the greater Hunter, will experience extreme fire danger on Tuesday.

“We need everyone to ensure they have got their plans, and a plan isn’t just about being at home,” NSW Rural Fire Service commissioner Shane Fitzsimmons said. “A plan is about when you’re travelling. Whether you’re out visiting loved ones, or out taking a break somewhere, spending time with family. Have the bushfire survival plan relevant to where you are.”

On Sunday the prime minister, Scott Morrison, announced that volunteer firefighters in NSW would be eligible for compensation for loss of income and said assistance would be extended to other states if requested.

• Australian Associated Press contributed to this report