Sixty prisoners are "actively involved" in the disturbance at HMP Ranby after twice as many inmates refused to return to their cells, the Prison Officers' Association (POA) has said.
At around 12.30pm 120 prisoners refused to return to their cells. They have taken control of a unit.
We have got national resources at the prison trying to establish a surrender plan. We know 60 prisoners have been actively involved.
Mr Travis said today's disturbance was "no surprise" to the POA.
It's all down to chronic staff shortfalls and a management that are hell-bent on delivering things they can't deliver safely.
Prisoners are saying 'We're not dealing with this'. They will react.
More top news
ComRes polling agency chairman says the next 100 days will be be gruelling in the most uncertain General Election that anyone can remember.
Pictures taken 70 years after the liberation of the Nazis' Auschwitz death camp echo the horrors of its Holocaust past.
Some 60 years after the brutal post-war communist regime 'disappeared' dissidents, the secrets of Poland's unmarked mass graves are exposed.