Firefighters have tackled a series of large gorse fires across two miles of Bodmin Moor.
Cornwall Fire and Rescue Service began to receive calls shortly before midnight about fires breaking out around Temple and Bolventor.
Fire officials said they suspected the fires were started deliberately, and said crews had a "challenging night".
At 07:30 BST they said the fires had been put out, but crews were still monitoring the scene.
Stuart Whitworth, of Cornwall Fire and Rescue Service, said the fire had started on both sides of the A30 and "that would indicate that this was probably a deliberately-set fire".
"Crews have worked very hard to extinguish all the fire fronts," he said.
"It really is a very difficult operation putting out wildfires overnight in treacherous conditions, with bogs and marshes."
About 80 firefighters tackled the blazes at their height, but crews later left the scene.
Olivia Tomlin tweeted that the "huge gorse fire" in three sections was close to houses and livestock and a main road, the A30.
Drivers on the A30 around Bolventor were warned by police to take care as smoke billowed from the fires, and fears were raised for homes and livestock.
Fires reported on Bodmin Moor near Temple and Bolventor please take extra care on the A30. Smoke currently not effecting carriageway however wind direction shift may soon change that. Fire service in attendance pic.twitter.com/tv9c8IOWZp— Alliance RPT 📱+🚗=❌ (@RoadPolAlliance) April 18, 2019