Grampians National Park fire grows from 500 to 5000 hectares in ...

Properties have come under threat in the Grampians National Park after a bushfire ripped through more than 5,000 hectares in just 24 hours.

At 7am yesterday the blaze on Yarram Gap Road had burned 500 hectares after it was sparked by multiple lightning strikes. 

This morning the fire has spread across 5,391 hectares of bushland. 

An emergency warning to leave immediately has been downgraded this morning to watch and act, prepare to leave, for Grampians, Mirranatwa, Victoria Valley and Jimmy Creek. 

Areas east and south of the fire including in Mafeking, Dunkeld, Bornes Hill, Willaura and Moyston are under an advice warning — residents are urged to stay informed.

In February this year catastrophic bushfires destroyed 46 properties in the Pomonal, Grampians area. 

A relief centre is now open at Sterling Place in Dunkeld for those evacuating the fires. 

Adrian Field is based in Mirranatwa, a town on the western side of the fireground, and has watched the situation unfold over the past day.

"At the moment it's pretty calm because there's no wind, but there is a lot of smoke around. But it's going to get warm later," he said.

"We're not really looking forward to that."

A fire in the Grampians National Park is burning out of control. (Supplied: Vic Emergency )

Mr Field said he was concerned about potential changes in wind direction to come.

"We are about a kilometre from the fire front," he said.

"The pace of this fire … it was incredible. It takes hold pretty quickly.

"I must admit it came as a bit of a surprise. I saw the fire yesterday morning … but within six hours, it was roaring. At that point I thought I was on the verge of getting out, but then the southerly breeze took it out."

Incident controller Peter Brick told ABC Ballarat Breakfast Radio there was a "significant" run of fire over the last day.

"It's grown nearly ten times in size, which is significant," Mr Brick said.

"What it tells us is the vegetation is really dry, you've had very low rainfall … it did pop out into some private property in the Mirranatwa area, up in the Victoria Valley."

One property in the area had been in the direct line of fire, but Mr Brick said there were smaller sheds in the vicinity, and farms.

"Unfortunately we've had reports that a few sheep are deceased, they got caught in the fire. Agriculture Victoria vets will head out there today."

Fire crews have worked tirelessly to keep the blaze within the national park. (Supplied: CFA South West Victoria)

He added crews overnight reported that the fire activity began to subside. 

"We have another three strike teams going in this morning … Where we did see the fire continue to grow is back in the park area, at the north and southern end.

"It's burning up on the Serra Road, it's expected to cross the road sometime this morning."

CFA state agency commander David Harris told the ABC crews worked tirelessly overnight.

"During the evening we had a really strong south-easterly wind push the fire from the Serra Range out into the Victoria Valley," Mr Harris said.

"It was quite a difficult night for our firefighters … In total we had about 188 firefighters out battling the blaze."

Mr Harris said while things were looking better today, Friday would be another difficult day. 

"Conditions will ease today, but we are expecting hot and windy conditions forecast tomorrow for Friday with extreme fire behaviour forecast."

A bushfire at Pomonal, also near the Grampians, caused property losses in February. (Supplied: Trevor Andrei)