Police investigating the brutal stabbing of a mother and son in a Grey Lynn dairy robbery have revealed a second person may be linked to the attack.

Police investigating the aggravated robbery want to identify a second person they believe can help them with their inquiries.

Detectives also want to speak to anyone who was near the Hylite dairy on Great North Rd about 7.15pm on Tuesday.

"Even if you think you didn't see much, please get in touch," police said.

A 16-year-old has since been arrested and is in Auckland Hospital with injuries police say were inflicted during the robbery.

Meanwhile, the woman stabbed in the "unprovoked and violent" armed robbery could return home today.

Gita Patel and her son, Siddharth, were seriously injured in the robbery.

Siddhart was initially in a critical condition but his father, Navin Patel, today told the Herald he was now stable.

However, his wife had since improved, despite suffering a broken shoulder, and Navin said she could be home as soon as this afternoon.

Auckland City District Commander Superintendent Karyn Malthus described the robbery as "an unprovoked and violent attack".

Navin Patel was visiting family in Canada when his wife and son were injured and immediately flew home.

He said they were "doing fine".

He heard about what happened from his daughter, who rang him to say her mother had been involved in an "accident".

His wife would have to go back to hospital for further surgery next week, he said.

His son, who was stabbed about four times in the chest and stomach area, was now stable.

However, he would likely remain in hospital for a week or two as he recovers.

Patel said the couple had owned the dairy for 15 years and not had any trouble.

"I think it's just a one-off. I have been here 15 years and nothing like this has happened."