UPDATE: Several people missing as catastrophic bushfires rage across NSW and Victoria.

Read the latest here.

PREVIOUSLY: Fire has hit a Victorian coastal holiday town and people are being told to go into the water as warning sirens sound.

Authorities believe about 4000 people are still at Mallacoota, which was being hit by fire about 8.30am on Tuesday.

"Everyone is hopefully down on the foreshore in the water," Don Ashby told ABC on Tuesday morning as emergency sirens sounded.

"We've all been evacuated to the wharf. Got the life jacket on, ready to get in the water," one evacuee shared to Twitter .

The fire has cut power to the town, with AusNet Services reporting 5700 properties in East Gippsland without electricity due to the fires, and another 1800 in northeast Victoria also down.

Mobile and landline phone lines are also down in parts.

"It's not pleasant, it's pitch dark here and the emergency vehicles have disappeared from sight," resident and local community radio presenter Francesca Winterson told ABC Gippsland.

"The power's been out here a long time and we've run out of solar.

"My home's in the fire path, I won't have a home, that's just the way it's going to be, we have to try and be calm."

Properties have been lost in Victoria's east as out-of-control bushfires rage, but it's too early to confirm how many, Emergency Management Commissioner Andrew Crisp says.

The fires grew rapidly overnight due to winds and lightning strikes and have ripped through more than 200,000 hectares in Victoria's East Gippsland, it was estimated early on Tuesday morning.

"There are property losses and there's property losses across East Gippsland, but at this stage it's too early to confirm in which particular locations," Mr Crisp told ABC News.

Seven emergency warnings, the highest alert, remain in place across East Gippsland and there is another in place for a fire straddling the northeast Victoria-NSW border at Walwa/Corryong.

Three strike teams are looking after thousands of people still believed to be in coastal Mallacoota, Mr Crisp said.

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"We are naturally very concerned about communities that have become isolated and to get an appreciation about other losses there could be we'll be putting helicopters up doing reconnaissance flights," he said.

Incident controller Chris Eagle told ABC Gippsland that lightning in the region sparked hundreds of new fires overnight.

By Monday evening, as temperatures soared and the fires started creating their own weather systems, about 1000 firefighters were working on the blazes.

"The satellite took an image of some of the heat tracks, it's several hours old now, but it's probably close to at least 60 per cent larger than it was yesterday, so much, much larger and that starts right up north of Gelantipy," Mr Eagle said.

Towns including Cann River, Bruthen and Orbost had been impacted by the fire and assessment teams will be sent to survey the damage.

The Princes Highway is closed between Bairnsdale and Genoa. The fire has also crossed Great Alpine Road at Ensay.

In the video below: Melbourne fire emergency

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A cool change swept through the region after extreme heat on Monday, but windy conditions remain, further fuelling the fires and spreading ash.

Mr Eagle said the fires were generating their own wind systems, which delayed the arrival of the cool change.

Victorian Premier Daniel Andrews attended a briefing at the State Control Centre, cutting short his holidays.

Fireworks displays planned in the region for New Year celebrations have been cancelled because of the fire risk.