The fire broke out across a stretch of land near Lochs Road, Isle of Lewis, on Saturday, 13 February.
Three appliances are currently in attendance tackling the flames as residents in the area have been warned to stay indoors.
A spokeswoman for Scottish Fire and Rescue Service (SFRS) confirmed the fire has spread across a moorland and crews are still on the scene.
It has not been confirmed what caused the fire.
A spokesman from Western Isles police said: “Emergency services are in attendance at a fire on Lochs Road, Isle of Lewis.
"Residents in the surrounding area are asked to please stay inside and keep their windows and doors closed.”
Earlier this week crews were called to reports of a wildfire at Market Stance, Balivanich, on the Isle of Benbecula, at around 3.30pm on Wednesday.
Three appliances attended the scene, and the fire was said to be about 1,000 metres wide.
A day later on the Isle of Harris, the fire service was alerted to a wildfire just after 6.30am on Thursday at Horsacleit.
The SFRS sent two appliances to the 1,600-metre-wide blaze.
No casualties were reported in either incident.
SFRS area commander Bruce Farquharson warned on Wednesday that despite the wintry conditions at this time of year, there is typically a large volume of dead, bone-dry vegetation which “essentially acts as a fuel for fire.”
“We are asking the public to exercise extreme caution and think twice before using anything involving a naked flame,” he added.