“The reason is that we don't have control over the fire and there is oil and diesel on board. If it gets worse, there could be a severe development of smoke and gas,” rescue worker Terje Heldal told Norwegian broadcaster NRK.
It was not immediately clear what had caused the blaze on the Strand ferry on Bomlö island, but its owner, Norled, said it could be related to current maintenance work which involved some welding.
“The fire likely started in connection with the welding work,” Norled spokesman André Utåker said.
According to TV station TV2, some 300 people have already followed the evacuation order and left the area.