Police are treating the unexplained death of a man following an incident at his ex-partner's house as a homicide inquiry until more is known about the death.
Waikato District Commander Superintendent Win van der Velde told a news conference officers were called to a Dinsdale address just before midnight on Tuesday by a woman saying her former partner was at her home and he was drunk.
He said the 26-year-old man, who had previously been served a trespass order on the property, entered the house and got into a struggle with the woman's new partner.
Two young children were present at Knightsbridge Place home.
When police arrived, the two men were found struggling on the ground.
The man was being restrained by police and was in handcuffs when he became unconscious.
Superintendent van der Velde said the man did not respond to CPR and died at the scene.
A 23-year-old man was admitted to Waikato Hospital. Police have not released details of his injuries, other than saying he was in shock.
Police say the investigation is in its very early stages and until more is known about why the man died, it will be treated as a homicide investigation.
A post-mortem will be carried out on Thursday.
Three investigations are being carried out; by a senior police officer from outside the region, the Independent Police Conduct Authority and the Coroner.