Police have asked for any video footage or witnesses of the assault at Bayfair Shopping Centre at 4.40pm yesterday.
Armed police swarmed the mall on Girven Rd and arrested a 16-year-old.
The girl has been charged with wounding with intent to cause grievous bodily harm. She was due to reappear in the Tauranga District Court next week, police said.
The victim of the attack remained in a stable condition in hospital.
A shopper, who did not want to be named, told the Bay of Plenty Times he understood someone had been stabbed.
The witness said he saw two teenagers running away from the Countdown store.
He went into the supermarket and saw a person lying on the ground bleeding. He believed they were a teenager. He said Countdown workers were helping the injured person.
A staff member of a nearby business said he saw a female being put onto a stretcher and taken to an ambulance.
“There were also a group of students here who were crying.”
A reporter at the scene could see armed police near the Countdown entrance inside the shopping centre. Trolleys were barring the entrance to the supermarket. Members of the public were standing around in small groups inside.
A Woolworths New Zealand spokesperson confirmed the incident occurred in its Bayfair mall Countdown store but said “our team are all safe”.
One shopper said on social media she was locked in a salon due to the incident.
“Omg locked in the salon due big stabbing incident in Countdown next door in Bayfair mall. Cops running round with big guns and other police and ambos here. In bloody Mt Maunganui!!! It’s happening all round the world!”
Police said they were investigating reports of an assault.
“Police believe the offender has left the mall area and we are making positive inquiries to locate them. One person has been seriously injured.”
A St John spokesperson said they sent two ambulances and two managers to the Mount Maunganui mall at 4.40pm.
They took one person to Tauranga Hospital in a serious condition.