Firefighters across Victoria and New South Wales are battling to contain huge blazes burning across the country's south-east, as a wind change that initially fanned erratic fires brings a brief reprieve.

Key points: In NSW erratic fire conditions have been predicted well into the night

In NSW erratic fire conditions have been predicted well into the night Rain in Victoria has been enough to extinguish so-called "campaign fires" but authorities warn forecast storms could cause flash flooding

Rain in Victoria has been enough to extinguish so-called "campaign fires" but authorities warn forecast storms could cause flash flooding A "mega-blaze" formed in the Snowy Mountains area and joined with a fire in Victoria's north-east

In Victoria, a bushfire in the Alpine region around Brookside, Buckland, Mount Buffalo and Buckland Junction has been escalated to emergency level, while rain elsewhere in the state has brought some reprieve to crews fighting other blazes.

The Alpine fire has been burning for a number of days, but has changed to a north-easterly direction and is now moving downhill into the Buckland Valley.

In NSW, light rain has fallen across the state and winds that predicted to whip up fires south of the Great Western Highway overnight were not as strong as expected.

The NSW Rural Fire Service (RFS) declared the South Coast "open for business" after assessments today.

Visitors may now return to areas of the Shoalhaven and South Coast.

The RFS Commissioner said there was no substantial damage to properties and no loss of life from yesterday's blazes.

"We're extremely relieved," Shane Fitzsimmons said.

"We had the benefit of visiting teams the day before yesterday and the investment in strategy … to limit their potential for spread under yesterday's conditions has really yielded dividends."

The Erskine Creek fire was burning out of control to the south of Wentworth Falls, but a forecast southerly change that was predicted to hit between midnight and 3:00am did not eventuate across the fireground, which eased fire activity.

NSW RFS said crews today worked to strengthen containment lines and used more favourable conditions to undertake backburning.

The change had been expected to push the fire towards Leura and Wentworth Falls, with residents told to make final preparations to protect their properties.

Erratic fire conditions were predicted well into the night in NSW. ( ABC News: Brendan Esposito )

Elsewhere, a "mega-blaze" formed about 9:00pm as severe weather conditions fanned fires in the Snowy Mountains area.

Commissioner Fitzsimmons said crews would work to exhaust fuel loads feeding the new blaze, which resulted from the Dunns Road and Green Valley fires joining.

"In a way, when they touch up, it is a good thing because they're running out of fuel," he said.

"But … we have seen the fire, the Green Valley fire head into Victoria. It has come back in towards NSW. So too has the Dunns Road fire.

"The only available viable containment strategy is to tie them together and burn out the available fuel around them."

Tonight there are four watch and act alerts in NSW, with the Erskine Creek fire downgraded to advice in the Southern Highlands area near Bundanoon.

Earlier, the Bureau of Meteorology (BOM) in NSW said forecasters were seeing an "increase in bushfire risk as the strong southerly change continues to make its way north through the night".

"The gusty winds may make local fire behaviour erratic as they hit the different blazes."

Flash flooding fears in Victoria's firegrounds

Along the Alpine border of the states, the NSW "mega-blaze" met with the northern tip of the Corryong fire which has razed homes and forced evacuations in Victoria.

In the East Gippsland and Alpine communities, Victorian firefighters faced strong, gusty and unpredictable winds late last night as the cool change moved through.

Victoria is still under a state of disaster. ( Facebook: CFA/Jacob Carracher )

It had been a nervous wait for people in Victoria's Alpine towns, but conditions eased overnight as the BOM cancelled its severe wind warning alert.

Authorities warned the danger was "far from over" as exhausted crews worked to use the milder conditions to contain fires across the state's east before temperatures rose again.

Rain in parts of Victoria has given firefighters a reprieve from horror conditions, but forecast storms are now threatening to cause "exceptionally dangerous" flash flooding in fire-affected areas next week, authorities said.

Rain has fallen on firegrounds in parts of East Gippsland, where a huge blaze has been raging for weeks, but other areas missed out on significant falls, including the north-east and fire-ravaged Mallacoota in the far-east.

Storms could hit mid-week

The rain has not been enough to extinguish the large so-called "campaign fires" burning across much of Victoria's east, but will allow fatigued crews to be rested while the immediate danger subsides.

Authorities warned the wetter weather would bring with it the risk of severe thunderstorms, which could lead to more risk on the firegrounds.

"Which again sounds bizarre in this situation where you've got fire, but [there is the] potential for flash flooding and also lightning," Victoria's Emergency Services Minister Lisa Neville said.

Fires continue to burn near Doctors Flat and Swifts Creek. ( DELWP Gippsland )

Storms are expected to hit the west of the state on Wednesday or Thursday, before moving across Victoria and into fire zones.

Ms Neville said flash flooding would be "exceptionally dangerous for our firefighters and emergency service workers".

"In the past, we have seen deaths as a result of those conditions," she said.

Rain reached Swifts Creek in East Gippsland's Tambo Valley on Friday. ( Supplied: CFA )

Fly-in, fly-out tradies

More than 30 local tradespeople were flown into the fire-affected Upper Murray, landing in Corryong today the assistance of the Australian Defence Force (ADF).

It will save tradies from travelling a seven-hour round trip each day from Albury/Wodonga and reduce the time needed to fix the main power line.

More than 17 power lines were downed as the fire tore through the area on New Year's Eve.

A generator has been supplying some power to the town, but many properties in outlying areas remain without power.

Space to play or pause, M to mute, left and right arrows to seek, up and down arrows for volume. Watch Duration: 53 seconds 53 s RAAF brings in tradies to fire-hit Corryong

Alpine region could remain closed to tourists for weeks

The Great Alpine Road remains closed between Cobungra and Germantown due to fires burning near Mount Hotham.

Victoria Police and the ADF doorknocked in the tourist town of Bright and nearby communities of Harrietville and Wandiligong after an evacuation warning was issued on Friday, and said most people had left the area.

Black bushfire smoke hung ominously over the Mount Hotham skyline last night. ( Supplied: Tom Pelly/Mount Hotham Resort Management Board )

Firefighters are using the cooler conditions to plan backburning operations to try to secure properties in the region.

It could be several weeks before tourists are invited back into Bright and other Alpine towns, which are usually bustling with tourists at this time of year.

A team of 24 US firefighters is expected to work in the Mount Buffalo area to protect property today.

Paul Bates, the incident controller at Ovens, said the historic Mount Buffalo Chalet is "all good" after earlier fears it could be destroyed.

"Someone said it has survived many bushfires."