More than 50 inmates reportedly took over part of a prison wing. The incident broke out at HMP Northumberland in Morpeth at around 7.30pm yesterday.
Prison Officers Association general secretary Steve Gillan told the BBC that there was a stand-off. He said last night: "We do not know what has sparked this major incident, but I do know that 50 plus inmates have taken over a wing," he said.
"We have teams from other establishments trained to deal with riots on their way. There is concerted indiscipline and our officers will try to contain it."
A spokesman for Sodexo, which operates the prison, said the situation has now been resolved and an investigation is due to be carried out into the incident.