Scores of firefighters have been tackling a series of large gorse fires spread over two miles of Bodmin Moor.
Police asked locals to be on the lookout for suspicious behaviour and report it after several blazes broke out overnight.
Witness Olivia Tomlin tweeted: “Another huge gorse fire up on Bodmin Moor. In 3 different locations, coming very close to the A30… people’s houses are so close to these fires and livestock are living in those fields.”
Cornwall Fire, Rescue and Community Safety Service said it began to receive calls to a gorse fire on Bodmin Moor shortly before midnight.
“On arrival, further resources were requested to deal with a mile long fire front,” the service said.
“Shortly afterwards, further calls were received to the Bolventor area with reports of a further fire were developing.
“It was quickly established that further resources were required to deal with 4 fire fronts spread over a distance of 2 miles.”
Over 80 emergency services personnel remained at the scene on Thursday morning.