Katterjåkk, a small town or "tourist station" in Kiruna municipality, reached 27.8C on Thursday. The settlement has not seen temperatures that high in nearly a century.
Nights have also been unusually warm, with temperatures not falling below 20C in several parts of Sweden, leading to Swedish media describing them as "tropical".
The balmy weather will continue in most parts of Sweden over the weekend, but then the worst of the heat is over, Sweden's weather agency SMHI reported.
"There is a high-pressure area settled over us," Lisa Frost at SMHI told news agency TT. "But during the weekend rain will pass over from the east, and it will become overcast with sinking temperatures."
Frost said temperatures over the next few days would hover between 20 and 25C.