"We have witness reports saying that people left the scene as emergency crews and police arrived," police spokesman Patrik Hamrén told the TT news agency.
RELATED GALLERY: Click here for images of the blaze
The fire at the Sigtunahöjden conference and hotel, located about 30 minutes north of Stockholm near the historic lakeside village of Sigtuna, was discovered shortly after 7pm on Wednesday.
The blaze completely destroyed the 5,000 square-metre conference centre and restaurant, but the hotel was left more or less intact.
The fire reportedly started in the kitchen, and took most of the night to bring under control.
No guests were staying in the hotel at the time of the fire, and no injuries were reported.
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