After seeing thick black smoke rising into the air above the mountain, firefighters pursued Ben Lomond.
The alarm went off around 2:15 p.m. that day, and paramedics were dispatched.
Scottish Fire and Rescue units are currently fighting the flames, which are believed to stretch over a kilometer in front.
The National Trust for Scotland said in an online statement that the fire was caused by a cigarette that was dropped in the area an hour after the fire started.
“The fire is spreading to the area where the natural regeneration of the forest has begun,” he added.
They also warned Hillwalker that the Ptarmigan route had become unusable and that there was no way down the mountain using that route.
A spokesperson said: “There is an ongoing wildfire in Ben Lomond.
“Please avoid this area until further notice.
“The fire is progressing along a kilometer ahead and appears to have been caused by a drop of a cigarette in the last few hours.
“The natural regeneration of forests is burning areas that are just beginning.
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“For the time being, there is no way down the Ptarmigan Road.
“Thank you for your understanding and support so far.”
The Scottish Fire and Rescue Service confirmed that members of the scene were still fighting the blaze.
A spokesperson for the Scottish Fire and Rescue Service told the Daily Express:
“Operators are currently monitoring the fire and evaluating the best options for extinguishing the fire in difficult terrain.”
Recently we talked about a man being rushed to hospital after a fire broke out in a block of Glasgow apartments.
First responders rushed to the scene on Tinwald Path after the alarm went off shortly after 8pm last night when a fire penetrated the building.
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