A husband and wife are fighting for their lives after allegedly being stabbed in a home invasion by a stranger, who is also in hospital after being shot by the 75-year-old man.

Police are baffled about the motive for a 34-year-old man allegedly breaking into the couple’s home in Torrington, in northern NSW, before stabbing them about 12.15am on Thursday.

The man, who police say did not steal anything from the couple, allegedly left the home after the stabbing. The husband was then able to call emergency services before the alleged invader tried to return.

He was met by the husband holding a gun. The 75-year-old shot the alleged attacker in the abdomen.

The accused man was taken to a nearby hospital, where he was in a serious but stable condition on Thursday.

Both the 75-year-old and his 72-year-old wife were flown to hospital on the Gold Coast. They remain in critical but stable conditions.

Their alleged attacker has been charged with two counts of wounding with intent to murder.

Detective Superintendent Chris McKinnon said police were not aware of a motive for the alleged attack, nor why the 34-year-old returned after initially fleeing the property.

He praised 75-year-old for being able to get his registered long-arm weapon, despite a stab wound. McKinnon said the man was within his rights to shoot his attacker in apparent self-defence.

“He certainly did his best, obviously under very difficult circumstances, to defend himself and his partner – quite impressive he decided to do that given the extent of the injuries he suffered,” he said.

“A person is entitled to use reasonable cause to defend themselves [and] this male had obviously received quite critical injuries up to that point.”

But police remain puzzled as to why the couple were targeted at all.

The alleged attacker is not accused of stealing any items from the house, nor is he suspected of having been at other nearby properties.

Police do not believe the couple knew their alleged attacker.

“This is a very rare occurrence, this is generally a fairly quiet regional location,” McKinnon said.

“But I would certainly encourage people to ensure they are secure in their own premises, they’re able to lock their doors, and be aware of people who aren’t from that area.”

Norm, who said he was the 75-year-old’s lifelong “best mate”, said the couple lead a “peaceful, calm” life at their rural property, and “wouldn’t hurt a fly”.

“Some mongrel comes in and does this to him … they’re bloody crook, I cannot believe [it],” Norm told 2GB radio.

“They put fruit out the front for people to come and get, so they can look after their neighbours and all of this stuff, bloody hell.”

The 34-year-old remains in custody and will face a bail court on Thursday.

-with AAP