By 1pm the fire service had extinguished the fire, just 45 minutes after the police received the first reports that a truck was on fire.
"Fifty-five people have been taken to hospital for checks. That's every single person that's been evacuated," police spokesman Jørn Lasse Refsnes told the agency.
The cause of the fire remained unknown, he added.
The tunnel, opened on 17 December 1991, connects the village of Gudvangen by Nærøyfjord with the Undredalen valley.