Firefighters in Graubünden were still battling the flames on Wednesday morning after strong winds fuelled the “large scale” fire in a wooden area between the villages of Mesocco and Soazza, police said in a statement.
The fire, which covers an area between 600 metres and one kilometre, was reported shortly before 6pm on Tuesday evening.
The A13 motorway was shut at 7.30pm due to the danger of rockfalls caused by the fire, and is expected to remain closed until at least Wednesday afternoon.
Four people were evacuated from houses in Mesocco, around 500 metres from the fire, and further evacuations are expected, police said.
Some 60 firefighters and rescue workers battled the fire overnight, a process made harder by the difficult terrain and the darkness.
The cause of the fire is as yet unknown.
Elsewhere, Some 29 people were evacuated by helicopter in the canton of Ticino after another forest fire broke out on Tuesday, Swiss media reported.
On Wednesday morning Ticino police said the fire, in the Monte di Doro region, was started by four adolescents who lit a campfire.