Man dies in police custody after retirement-home arrest

"The man was secured in the rear cage of a police vehicle," police said in a statement.

"A short time later the man was observed by members to have laboured breathing."

Officers began CPR before paramedics arrived, taking the man to Royal Darwin Hospital where he was declared deceased about 10:10pm.

"The formal cause of death is yet to be determined and the deceased is yet to be formally identified," the statement said.

A crime scene has been established at the police vehicle and the arrest's location.

The death is being investigated by the NT Police's major crime section detectives with oversight from the Professional Standards Command.

"Police are also investigating this matter on behalf of the coroner," the statement said.