The Northern Territory Police Force (NTPF) is investigating a death in custody that occurred in Casuarina overnight.

Around 8:40pm, the Joint Emergency Services Communications Centre received a report that a man had damaged window louvres and assaulted a woman at the Tiwi Gardens Retirement Village in Casuarina.

Police attended the scene and located a man in the vicinity, who was arrested without incident.

The man was secured in the rear cage of a police vehicle. A short time later the man was observed by members to have laboured breathing. St John Ambulance were contacted while police began CPR.

St John Ambulance members attended and conveyed the man to Royal Darwin Hospital where he was later declared deceased at 10:10pm.

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

A crime scene was established at the police vehicle and the location of arrest.

The NTPF Major Crime Section Detectives are investigating the death with oversight from the Professional Standards Command.

Police are also investigating this matter on behalf of the Coroner.