Bleeding heavily from a broken eye socket and multiple machete slashes to his head, Senior Constable Bruce Mellor curled up into a ball to try to protect himself from further blows.

As he lay there on the side of the road with continuous blows raining down on him, the experienced Highway Patrol officer thought he would die and could only hope his training would get him through it.

Mr Mellor had just stopped a Mazda that was being driven erratically near Taihape on Saturday morning and had no idea anything was wrong as he walked back to his patrol car to check the teenage occupants' details.

"He didn't see it coming, he had no inkling at all," said Police Minister Judith Collins after visiting the injured officer in hospital yesterday.

"He was taken by surprise, slashed across his face and he fell to the ground ... He thought he was going to die."

The attack was so vicious Mr Mellor's cellphone, which was tucked into the top of his stabproof vest, was sliced along with many other parts of his body.

A passing motorist found him lying in a pool of blood and he was rushed to Palmerston North Hospital with multiple skull fractures, broken teeth, a broken eye socket, broken jaw, cuts to his arms and a badly damaged finger.

Yesterday Mr Mellor's eyes were almost swollen shut as a result of the repeated blows to his head.

But, despite suffering what were initially feared to be life-threatening injuries, Mr Mellor was last night in a stable condition and even "cracking a few jokes", colleagues said.

"He's in pretty good spirits but he's still not out of the woods," said Detective Inspector Chris Bensemann. "They are still monitoring the brain bleed every fours hours. He's still got those fractures there and he's got a lot of staples and stitches all over his face."

Mr Mellor can remember what happened, possibly because he never lost consciousness, but police have not yet pushed him on the details as the focus at the moment is on his recovery.

"That's something we will do when we need to do it and when his energy levels are all right."

Mr Bensemann said the two teens who fled in the Mazda after the attack crashed nearby and were arrested.

An 18-year-old has been charged with unlawfully taking the car, attempted arson of it and assault. A 14-year-old, who is now in CYF's custody, is charged with unlawfully getting into the car, attempted arson and assault.

Further charges are being considered and both males are due to appear in Whanganui District Court today.

Although it is early days, Mr Bensemann said Mr Mellor did not appear to have been put off the job and it seemed like he "just wants to get back on the horse".

He told Radio new Zealand this morning he did not know Mr Mellor well, but that he was "well liked".

"He's still got a sense of humour. He's a lucky guy."

Mr Mellor, based in Waiouru, mainly works on highways between Taihape and Waiouru and police say it wasn't unusual for him to be working on his own when the attack happened.

He has been in the job for 35 years, first with the Ministry of Transport, then with the police, but this is the first time he has been injured.

Ms Collins said she was shocked by the extent of his injuries.

"It's horrific and I have seen quite a few police officers who have been shot and attacked but I don't think I've seen anything that looks so horrific before," she said.

"He seriously looks like he's out of a horror movie, it's that bad."

Mr Mellor told the minister his training, which meant he knew he needed to roll into a ball, had probably saved his life.

Locals in the area where Mr Mellor works have described him as one of the nation's "best country cops" and a Facebook page has been set up for people to leave messages of support for him.

One friend told the Herald Mr Mellor was not the type of person to feel sorry for himself and would probably "make small of what happened to him". She doubted it would prevent him from returning to his job.

Meanwhile, the vicious attack has reignited the debate about whether police officers, especially those on the frontline, should be armed.

Mr Bensemann told Radio New Zealand Mr Mellor did not have access to a firearm.

Police Association president Greg O'Connor said the time had come to carry firearms.

"New Zealanders have just got to accept that they have got to empower their police because if the police can't defend themselves and the police aren't safe the public can hardly feel safe themselves," he said.

He didn't accept comments that it wouldn't have made a difference if Mr Mellor was armed, saying the situation may have unfolded very differently if the alleged offenders knew he was carrying a gun.

Ms Collins told Radio New Zealand extra staff for rural police patrols was a priority regardless of the cost.

"It is a very dangerous, particularly for rural officers ... those officers are alone in remote places and frankly it is sheer luck Bruce is alive," said. "Attacks on police are becoming more frequent and more vicious.

"It is very important we put the safety of our officers before cost, quite frankly."

Police Commissioner Howard Broad is due to meet the minister today to present the findings of a report that was commissioned after two police officers were shot in Christchurch this year.

Ms Collins is expected to comment further once she has seen the report.