A FIRE burning underground in tree roots caused a major blaze at Redesdale on Tuesday, according to the CFA.
Fire investigators attended the fire's ignition point at Ford Road on Wednesday.
CFA district two spokesman Chris Jacobsen said a previous fire at the site had laid dormant before flaring up again.
“It looks like it’s been buried underground from a previous fire and escaped with the change of wind,” he said.
“The fire will burn in the roots of the tree and you can’t see it.
“They’ve checked to see if it’s out but it’s continued to burn below soil level, and eventually burnt through to the surface.
“It’s not common, but it’s not unheard of.”
The fire followed a blaze at Malmsbury earlier on Tuesday.
The town was placed on an emergency warning with fears the fire would threaten the town and its residents.
CFA operations manager Mark Gilmore said it appeared a falling branch had struck powerlines and started the fire.
“That’s being followed up at the moment,” he said.
“It was investigated on Wednesday.”
Mr Gilmore said there did not appear to be any suspicious circumstances with the fire.
The Redesdale blaze had moved in a northwesterly direction from Newnhams Lane towards Myrtle Creek.
Fire fighters managed to contain the fire at about 9.20pm and an emergency warning was downgraded to an advice message.
A CFA spokesman had said the location of the fire had helped contain the fire.
"It was burning near a river so that helped box it in," he said.