One concert-goer fell onto two people from a height into the open foyer on the ground floor at the Uppsala Konsert & Kongress hall near the capital, Stockholm on Tuesday, police said.
The person who fell and one of the people they hit died while the third person has been rushed to hospital with non-life threatening injuries.
Police have yet to identify the victims.
The incident happened just 30 minutes before the concert was due to begin.
Police spokesman Magnus Jansson Klarin told the AFP news agency: “We received a call about someone having either jumped or fallen from a high altitude.”
Police said it was too early to say whether a crime had occurred.
There were around 1,000 people attending the concert and initially the hall had to be closed by police to question witnesses at the scene.
Events company MTLive - who organised the gig - said “everyone is in shock” in a statement on their Facebook page, according to the BBC.
The statement read: “Unfortunately, we have to announce that a terrible event has happened. What we know is that someone jumped [or] fell high in the arena and hit other people.
“Right now we don’t know much more, everyone is in shock.”
It comes as Abba will drop a new album for the first time in more than 40 years on Friday marking their reunion.
