Authorities suspect a series of large gorse fires on Bodmin Moor were started deliberately.
Scores of firefighters worked to tackle the blazes through the night, with flames spreading two miles over moorland in Cornwall.
Witness Olivia Tomlin tweeted flames came "very close" to people's houses, livestock and the A30 road.
Emergency services first received calls shortly before midnight on Wednesday, with crews leaving the scene on Thursday morning.
Stewart Whitworth, of Cornwall Fire and Rescue Service, said early indications,suggest the fire was of a "suspicious nature", adding: "There are very few natural causes of wildfire at 10 to midnight."
Flames were burning in "multiple" areas on either side of the main A30 road, he added.
Around 70 firefighters tackled the fire with beaters for around seven hours before the blaze was extinguished at around 7.30am, he said.
Police asked locals to be on the lookout for suspicious behaviour.