The robbers broke into the two-story house in the Norrtälje suburb of Rimbo at around 11pm on Saturday evening as the four people, two couples, were having a party on the ground floor.
The four partygoers were threatened, but according to police were not subjected to any violence. Their hands and feet were tied with electric cable and they were locked in a toilet while the thieves ransacked the house.
“This happened around 11pm according to the victims. The thieves were then in the house for some time before they left. The victims eventually managed to wriggle free and call the police,” Susanne Abrahamsson at Norrtälje police told news agency TT.
Police received the call at around 2am.
It was as yet unclear on Sunday morning what the thieves had managed to steal, but a safe was found forced open.
“There is talk about some art, but if it is a question of a large amount or just a few items I do not yet know,” Abrahamsson said.
The robbers were masked and the four people in the house at the time have told police that they could not identify them. Further interviews will be undertaken during Sunday.