Two prison officers have been taken hostage at a high-security facility in Eskilstuna, west of Stockholm, since Wednesday afternoon.
Two inmates blockaded themselves in a room at the Helby prison with two prison officers at 12.30 pm and covered the CCTV cameras, the Swedish Prison and Probation Service said.
The inmates are serving sentences for murder, acting security chief Jörgen From Nordin told a local Swedish news agency.
He added that the negotiators and a police task force were at the scene and described the situation as “frozen”.
Local media reports said the inmates are demanding a helicopter for their escape.
“This is a very serious incident,” the Swedish Prison and Probation Service said.
Helby is Sweden’s largest security classification, Class 1 prison - 10 kilometres west of the town of Eskilstuna.
Includes reporting by AP