A 33-year-old diabetic Aboriginal man died after being taken twice from the Perth watch house to hospital for medical assessment, in the police custody.

An investigation has been launched into the conditions, in which he died this Sunday, by the internal affairs unit of the police.

He was arrested on Saturday due to breaches of a violence restrictive order after police were called to a domestic dispute in Belmont, in the city's southeast. He hails from Huntingdale in Perth's south.

Detective Superintendent Tony Flack, while offering sympathies to the kith and kin of the deceased, said, "Any death of a 33-year-old person is upsetting and tragic for all".

As soon as the man was arrested, he was sent to the Royal Perth Hospital for medical checkup as they came to know about their diabetic condition.

Though he returned to the hospital after getting the treatment, on the Sunday afternoon, a nurse noticed a spike in his sugar level again.

He got unconscious at about 10:20 pm, and after a few attempts of resuscitation, he was taken to the hospital where he died at about 11:30 pm.