The man, in his 40s, was found early this morning unconscious and not breathing.

"Officers performed cardio-pulmonary resuscitation at the scene until ACT Ambulance officers arrived, but the remandee did not respond," ACT Corrective Services Executive Director James Ryan said.

It is the first death in custody since the prison began accepting inmates in March.

"It is always regrettable when an incident of this nature occurs," Mr Ryan said.

"While the man’s family has been contacted, it is not

appropriate for further details to be released at this time."

"Matters of this type are subject to formal investigation processes, which have already been set in train."