Cumbria Fire and Rescue Service say a 'significant' hillside blaze may have been started deliberately.
Seven crews from across the county spent much of the night fighting a wildfire on fells, near Braithwaite, in the Lake District.
Emergency services were called to Newlands Pass, near Birkrigg Farm, Newlands, at 12:20am on Thursday morning
Firefighters tackled a massive fire which, at its peak, was 800m-long.
Specialists from Keswick, Ambleside, Windermere, Appleby, Millom, Sedbergh and Whitehaven spent hours trying to put out the flames, which they believe were started on purpose.
Nathaniel Hooton, Area Manager, Cumbria Fire and Rescue Service, said: “We are disappointed to see what has happened overnight as it could possibly have been avoided.
"Wild fires spread quickly, threaten local wildlife and tackling the fire takes a large amount of the Fire Service’s time and resources.
"This is especially important at a time when we are supporting the national effort to respond to the Coronavirus outbreak and focusing our valuable resources on helping our partners and supporting Cumbria’s communities and vulnerable people.”
The road between Buttermere and Braithwaite is currently closed.
Anyone with any information about this incident is asked to contact 101.