The blaze in Galloway resulted from a controlled burn on a farm near Newton Stewart in Wigtownshire on Sunday evening which became unmanageable.
Dumfries and Galloway Fire and Rescue Service said that it had been monitoring the situation overnight and that crews had been deployed to the fire at first light this morning.
It has been reported that 25 appliances are at the scene today.
Elsewhere, Highlands & Islands Fire & Rescue Service (HIFRS) warned of the dangers of controlled burning after it had to deal with a wild fire in Ardnamurchan.
Ten appliances responded to the blaze between Portuairk and Achosnich, near Sanna Bay at the Point of Ardnamurchan.
Two properties had to be evacuated as a precautionary measure and firefighters were on the scene for more than 24 hours.
Billy Wilson, head of operations for the service, said: “We would encourage landowners that are carrying out controlled burning of vegetation to be fully aware of their responsibilities. This includes notifying HIFRS of any planned burning and having adequate personnel and equipment on site to deal with any unplanned fire spread safely and controlled”.
“Fires of this nature can rapidly spread to vast areas of moorland, forestry plantations and in some cases property, they are not only damaging to the natural environment, they cause a considerable drain on Fire and Rescue Service resources as well as putting firefighter’s safety at risk”.