Police administered first aid and ambulance staff were unable to revive the man.
He received police dog bites during the arrest, Mr Johnson said.
Police were investigating the Hastings attack, which occurred about 6pm on Thursday, and the death.
"Both of those incidents will be carefully considered along with background medical and other relevant factors," Mr Johnson said.
Police were waiting to inform other family members before releasing the man's name.
Mr Johnson said the cause of death would be established by the investigation.
"Whether there was a medical event or whether there were other factors at play, I'm unable to say. A post-mortem [examination] will be conducted with the intent of establishing those facts."
Asked if drugs or alcohol were a factor in the incident, he said: "There is evidence of alcohol in the car but that will be looked into further as part of the investigation."
The man's father was discharged from hospital yesterday and had spoken to police.
Police said they had recovered a "cosh" (a long blunt instrument) from the Hastings property. It was the weapon used in the attack on the father.
Mr Johnson said the dead man, who did not live in Hawke's Bay, was known to police and had not been in contact with his parents for some time before Thursday's confrontation.
"This was a tragic incident and we extend our sincere sympathies to the family of the man involved. There will be a thorough and robust investigation into what took place ..."
Bob Bird of Westshore told Hawke's Bay Today he was woken by barking police dogs at 2am. Six police cars and two ambulances were at a beachside carpark. He had watched emergency staff working on someone. "I watched them do CPR for half an hour. Then they put a white sheet over the body."
Mr Johnson said about 10 police staff were involved in the Westshore incident. None had been stood down as a result of the investigation.
NZME.