The woman who was stabbed on Anzac Ave this afternoon was known by her attacker, Auckland police confirm.
The serious assault took place around 2.30pm in Auckland Central and the man who assaulted the woman is in police custody.
"This was not a random attack and the two people involved are known to each other," Detective Senior Sergeant Scott Armstrong said.
"Police were on the scene quickly and there is no ongoing risk to the public".
An 18-year-old man is assisting police with their inquiries following the attack on the 18-year-old woman, who received serious injuries.
St John confirmed the woman was transported to Auckland City Hospital following the attack.
A spokeswoman for Auckland District Health Board told the Herald the woman's condition had not changed, and she is still in a critical condition.
Police said the victim's family have been notified and are being supported by police and Victim Support.
Police remain at the scene and will stay there into the evening to complete a scene examination.
Detective Senior Sergeant Armstrong thanked the public for their assistance and urged anyone with information to contact the Operation Pompano investigation team on 09 302 6557.
Earlier today, a witness said the attack happened outside the entrance to the Wilson Parking building at about 2.45pm.
Employees from a nearby store said they heard a woman screaming. They then heard a man screaming but didn't leave the store because they were attending to customers.
Bystander Abhi said he saw a woman lying down on the ground.
"I spoke to one of the ladies who witnessed it all," Abhi said.
"She told me it was a white guy, a tall guy, with some kind of kitchen knife in his hand. She saw him stabbing her in the back and in the front.
"All I saw was a lady lying down, we all went to see what's going on," the witness told Abhi.
Members of the public rushed to the woman's aid and tried to help with basic first-aid supplies. Police and ambulance officers arrived soon after.
When the Herald went to the scene this afternoon the woman's handbag and other personal items were still on the footpath.
First aid supplies, including scissors, a first-aid kit and paper towels were also scattered on the ground. There was blood on the footpath.
St John confirmed the woman had been taken to Auckland City Hospital.