The authorities were alerted to the mountain Melshornet in the coastal municipality of Hareid at 5 pm on Sunday.
A real storm had then set in, with thunder and lightning.
- We sent away the rescue resources we had and it eventually became an ambulance helicopter that was able to get up between lightning and thunder and pick up the injured person along with one of those who died, says rescue leader Borge Amdam to NRK.
The helicopter then returned to pick up the other person who died.
The third person, who survived, was taken to hospital with serious injuries.
Additional rescue efforts are underway in the same mountain area.
Authorities are urging people to stay away from or leave the mountains quickly.
Between 2 pm and 3 pm, lightning struck southern Norway more than 3,000 times, according to NRK.