Around 5pm on Saturday, a married couple, both 57 years old, and their son, 24, and daughter, 23, were all admitted to St Olav's Hospital.
The couple and their daughter suffered only minor injuries from the lightning attack, but the young man was seriously injured. He was taken to intensive care at the hospital where his condition is said to be stable. He received vital heart and lung rescue at the scene of the incident after having a heart attack.
Tore Kyllo, operation leader with the local police, confirmed to NTB: "It is a family of four that is struck. One of them got a cardiac arrest, but resuscitation made his heart beat again."
The lightning struck the family in the mountains around Lake Jølvatnet, over 1,000 meters above sea-level.
The family were able to notify the emergency services and initiate first aid to the young man until rescue services arrived.
Rescue leader Bjørn Jarle Åmlid said to Adressa.no: "An airborne ambulance from Dombås and a Sea King helicopter from Ørland were sent to the site. They localized the family in the mountains and brought them to St. Olav’s Hospital."
Locals and visitors to the area confirmed there had been a thunderstorm in the area at the time of the incident.
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Karl Olav Mærk, owner of holiday cabins at Lake Jølvatnet, said: "There had been a normal thunderstorm for this time of year."
Meteorologist Frank Dahlslett confirmed reports there were unusually high numbers of "fierce thunderstorms" across all of Norway on Saturday. There were 710 registered lightning strikes during a six-hour period, where 338 strikes hit the ground.