Police say a man who was found dead in the Papakura District Court cells this afternoon was alone at the time.
They say the man, who was 36, was in custody for charges of kidnapping, injuring with intent to injure, and assaulting a female.
He was arrested early this morning for breaching his bail conditions, which related to the charges.
Superintendent John Timms of Counties Manukau Police said the man had appeared in court today and had been remanded in custody.
Mr Timms said when officers entered his cell to move him, about 3.45pm, he was unconscious.
He said police and ambulance staff tried to revive him, but he was pronounced dead.
A full investigation was underway into the circumstances of the man's death, and it has been referred to the IPCA.