A 16-year-old is in police custody after the aggravated robbery of a Grey Lynn dairy last night.
Police said the youth had undergone surgery and it was likely charges would be laid in the next day or so.
The two family members involved in the stabbing have been described as "good people" who were caring and mindful of customers entering the store.
The shop on Great North Rd, that is known to many people in Grey Lynn as their local, is closed while police investigate the brutal attack.
A regular customer who brought flowers for the family tonight said the owners were wary about security and had been concerned about beggars and "unsavoury" characters who frequented the area.
"He is often seen standing in the doorway keeping a lookout for potential clientele, the woman told the Herald.
"He was worried about some of the unsavoury characters."
On Tuesday night a mother and her adult son were stabbed in the Hylite Dairy in what police called an "unprovoked and violent assault".
Detective Inspector Scott Beard said a male offender armed with a knife entered the dairy and waited until a customer left the store.
He then walked behind the counter with the knife and without warning attacked the owner.
"Family members tried to intervene at which stage a 62-year-old woman was stabbed and assaulted. The offender then fled from the dairy towards Turangi Rd.
"Two people received serious injuries and have undergone surgery and are in a
stable condition in hospital. The victims are related and are a mother and her adult son."
Addressing media at a press conference this afternoon outside the cordoned off store, Beard said it was not believed anything was taken during the attempted robbery.
Asked if a weapon had been found, Beard said investigators followed a trail of blood last night which led them to a weapon they believe was used during the attack
Looking through the store's window cigarette papers and pouch tobacco can be seen strewn across the ground behind the counter, near two pairs of slippers.
A white cardboard box was splattered with what appeared to be dark red blood stains.
Outside the dairy, a Grey Lynn woman brought a pink bouquet of flowers in the rain hoping to give it to the mother or the son involved in the attack.
However, the pair remained in hospital and the store was closed.
She told the Herald the owner of the dairy and his family were already very security conscious.
They were well known to the community and when her mother's card had declined while getting some groceries they had let her take them home and return to repay the debt when she could.
"It is just so sad this would happen to these good people."
The owner of Grey Lynn Fine Wines and Spirits said police had gathered CCTV footage from the store's front camera that showed the dairy entrance.
Someone had entered the wine store during the incident and asked an employee to call an ambulance because someone had been stabbed.
New Zealand Association of Convenience Stores executive director Dave Hooker said the level of violence in the attack was "disturbing".
Convenience store robberies had been increasing in recent years, which he believed was due to the rising price of tobacco.
"Over the past 24 months there has definitely been an increase. We saw about 700 in the 2016-2017 year, and this increased to about 1300 in 2017-2018.
"Dairy owners have a high level of anxiety around security."
He supported the government subsidies for fog cannons, and said there had been a greater focus from police on the issue.
So far about 60-70 dairies had taken up the offer for cannons, he said.
"But I would like to see the fund used more broadly, to include things like installing bollards, CCTV, strengthening windows and improving store lighting."