Police Minister Judith Collins, who visited Mr Mellor in Palmerston North Hospital this morning, told NZPA she had never seen such horrific injuries.
"It was a frenzied attack and he has sickening injuries, I've never seen so many staples in one place, it's unbelievable."
Given what he had been through, the Minister said, the officer was in "unbelievably good spirits" and was keen to get back to his home town of Waiouru, where he had been a police officer for the past eight of the 35 years he had been on the force.
"I'm just so pleased he's alive because I really did think he was going to die, and he said he felt he was going to die when he was on the ground being attacked with a machete. He thought that was it, it was all over."
As well as receiving deep cuts to his head and nearly losing a finger, he suffered a fractured jaw and eye socket, and had several skull fractures.
Mr Bensemann said that Mr Mellor's eyes are now completely closed due to swelling.
"I think the most telling of all the injuries, that provides you an appreciation of what he went through, are the horrific defence injuries," Mr Bensemann said.
Members of the public stopped shortly afterwards and rang police, but Mr Mellor was also trying to radio for help during the attack.
"It was really quite unexpected, it was a routine stop," Mr Bensemann said.
The constable's eyes were completely closed due to swelling caused by repeated blows to the head.
In response to the incident, Police Association president Greg O'Connor said it was time for every police officer to have access to firearms.
Preventing single patrols was unrealistic as it would mean virtually doubling the staff in most stations around New Zealand, he said.
Two youths, aged 14 and 18, have been charged with assault, unlawfully taking a motor vehicle and attempted arson and police were considering laying further charges.
The 14-year-old was placed in Child Youth and Family custody.
Both will appear in Whanganui District Court tomorrow.
Tributes for "Mr Desert Road"
The attack left two communities in shock - Mellor worked for more than two decades in West Auckland before moving to the central North Island plateau in 2004. Tributes flowed for a man who is known as "Mr Desert Road" and "your typical community cop".
Robyn Gregory, who lived near the site of the attack, said she had known Mellor for five years.
"He was all for the community. He's a caring and genuine guy.
"Whenever people break down, he's there making sure they get on okay. He's an absolutely lovely guy."
Stolen car owner Bianca Alani said sleeping through the theft meant she might have avoided a confrontation.
"It sounds like if one of us had tried to stop them we would have got into trouble," said Alani, 18.
Widow Sue Umbers said attacks of the sort suffered by Mellor instantly took her back to the murder of her husband, senior constable Peter Umbers who was beaten to death in a similar situation in 1990.
She said when she heard of Mellor's attack it made the death of her husband "feel like just yesterday".
Umbers was beaten to death with his own baton.
She felt for families of police officers who lived knowing they put themselves in grave danger and may not come home.
- Additional reporting: Associated Press, NZPA, Joanne Carroll and Leigh van der Stoep
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