The heavy smoke from the blaze has spread in the direction of local townland Moyra and forced a number of people to leave.
Up to 50 officers have been dispatched to the scene of the blaze which broke out a short time earlier.
Dozens of acres of gorse have already been destroyed.
At this stage there are no reports of any injuries or any damage to property.
The latest blaze alert comes just a couple of hours after Acting Fire Chief Bobby McMenamin revealed that most gorse fires across the county are now under control.
The fire at Muckish is being tackled by the army, the army helicopter which is dropping buckets of water on the fire and two fire brigades.
The fire is also coming perilously close to Glenveagh National Park which is just a couple of miles away.
As well as tackling the blaze it is understood that officers are also dampening down areas in its path to keep it from spreading.
“The Muckish blaze has whipped up a lot of smoke and that has been spread in the direction of Falcarragh.
“A number of houses have now been evacuated because of the smoke. People were beginning to feel the affects so they thought it was best to get out,” said a fire service source.