Almost 50 firefighters have been battling the grassland fire, near the A708 at St Mary’s Loch in the Scottish Borders this afternoon (Tuesday).
The fire has been burning since just after 5pm last night (26 March).
Although crews had made some progress in getting the fire under control overnight it began to spread again this afternoon.
Local sources suggested the fire could have been started by a spark from an area of controlled burning.
Seven pumping appliances are at the scene along with two specialist vehicles.
Firefighters from Lothian and Borders Fire and Rescue Service have been working in difficult conditions to bring the burning heather fire under control. Due to the steep hillside terrain they are on foot using beaters and water backpacks in a bid to put out the blaze.
A spokeswoman for the service said: “Gorse and grass fires are unpredictable and can get out of control and spread rapidly. This makes for a challenging job for firefighters trying to get the fire under control and anticipate potential spread. It can also be physically arduous for crews fighting the blaze on foot.
“The fire and rescue service urge members of the public to stay away from the immediate area, and remain vigilant at all times when they are out in the countryside. In dry weather such as we’ve had this week, take extra care to avoid starting a fire. Dispose of cigarettes butts properly, ensuring they are extinguished first and never leave glass bottle lying out.”