Two inmates barricaded themselves in a room at the Hällby prison together with two prison officers at 12.30pm on Wednesday and covered the CCTV cameras, wrote the Swedish Prison and Probation Service in an email sent to the TT news agency.

Acting security chief Jörgen From Nordin told TT the two inmates are serving sentences for murder.

He added that negotiators and a police task force were at the scene and described the situation as “frozen”. “This is a very serious incident,” he wrote.

A police spokesperson told The Local at around 4pm that they had a helicopter present at the prison. “Two inmates have barricated themselves in a space in the institution and in the same room there are two employees,” they said.

The Aftonbladet newspaper reported that the inmates had demanded kebab pizza to everyone in their block in order to free one of the hostages, but police would not confirm.

“There are currently several rumours circulating online but it is not something I can comment on,” the spokesperson told The Local.

Hällby, some 10 kilometres west of the town of Eskilstuna, is a class-one prison, the maximum security classification in Sweden.