Police are not revealing any information about the death or the circumstances surrounding it, other than that it happened about 8pm.

"ACT Policing Criminal Investigations is investigating the circumstances surrounding the death and a report will be prepared for the ACT Coroner," they said in a statement.

Corrections Minister Shane Rattenbury said the man's next of kin had been notified, but his identity would not be revealed on Sunday.

"On behalf of the ACT government, I would like to express my deepest sympathy to the family and friends of the individual. I understand this will be a difficult time for them and I ask that you respect their privacy," he said.

"Any death in custody is a tragedy and of deepest concern.

"I am advised that ACT Corrective Services staff were notified by a detainee who was concerned about the health of the detainee. I am further advised that no disturbances were reported around the time of the incident."

It follows the death in custody of Steven Freeman in May last year, which prompted an independent inquiry which found significant flaws in the prison system.

The specific cause of Mr Freeman's death is the subject of an ongoing coronial inquest, which is expected to resume in August.