Fire crews from Newquay, St Columb and Perranporth were called to a fire in a derelict hotel along the Narrowcliff yesterday.
People reported seeing smoke coming from both the rear and side of the former Narrowcliff Hotel shortly before 1pm.
Firefighters say they found a fire on the second floor of the building - and used a triple extension ladder along with breathing apparatus, main jet and thermal imaging camera to put out the fire.
A spokesperson for Cornwall Fire and Rescue Service said: "The cause of the fire was doubtful and incident details have been passed to Police."