A Northland police dog stabbed in the lung during a chase through dense bush is on a machine helping him to breathe but is expected to survive.

The German Shepherd named Gus was flown by police helicopter to a vet clinic in Auckland with his devastated handler about 8.30am yesterday.

Gus was connected to an apparatus that releases air from his punctured lung, with a bandage around his middle covering the stab wound. A bandage on his leg was holding a drip in place.

Gus's handler is remaining at his side at the vet clinic while the canine crimefighter continues his treatment.

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Police said due to the dog's bravery more serious injury to police officers was averted.

Northland's head dog handler, Sergeant Phil Kahotea, who has been a dog handler for 24 years, said his colleague was devastated by the serious injury to his "best mate".

The two had been sniffing out criminals together since 2009 and had represented Northland police at national Police Dog Trials.

Mr Kahotea said Gus was an exceptional police dog with a real strength for tracking. "His obedience combined with his excellent tracking skills makes him a top police dog," Mr Kahotea said.

"It's not only terrible for the handler and the family, but for all of the police staff in Whangarei who know this officer and dog." He said the dogs were treated like members of handlers' families and officers developed a special relationship with the dogs.

The drama began when police were alerted to a 37-year-old man believed to have been carrying a knife and a firearm at his Parakao home, 40km west of Whangarei, about 4pm on Wednesday.

Members of the Northland Armed Offenders Squad, along with detectives and frontline officers, went to the property.

The man was reported to have been in an agitated state and while officers were placing cordons around the man's property, the man had allegedly stolen a quad bike from another property and ridden off.

Police had chased the man, who had abandoned the bike on farmland and run off. AOS members and the police dog handler and Gus had started tracking the man through thick bush and the man was found about 4am. He had allegedly stabbed Gus and tried to stab the dog handler.

After a struggle police had arrested him. Gus's handler and another officer had carried him a kilometre through heavy bush and steep hills.

Following a special hearing in Whangarei Hospital yesterday afternoon a man was charged with aggravated assault on a police officer, attempting to kill a police dog, unlawfully taking a vehicle and assault with a weapon. The man was remanded in custody for a psychiatric report and will appear in the Whangarei District Court on October 14.

Whangarei/Kaipara Area Commander Inspector Tracy Philips said police staff had been faced with a dangerous and fluid situation with an unpredictable offender.

"One of our dogs has been injured during the incident and due to his bravery we averted more serious injury on our police officers," Ms Philips said.

"Gus is very much a part of our police family and we feel for the dog handler who has witnessed his dog getting seriously injured. Gus is trained to protect his handler and he did just that and has paid the price, but thankfully he has survived."

It costs about $60,000 to get a police dog operational.

There are currently 21 dog sections nationwide, made up of 120 dog teams. They are called out about 40,000 times per year.

Some 23 police dogs have been killed in the line of duty since 1972.

The charge of killing or injuring a police dog is punishable by a maximum of two years' jail and/or a $15,000 fine.