Police District Commander Naila Hassan said the suspect in the Auckland attack was in custody, no motive for the attack was immediately apparent.
No cases of omicron have been found in New Zealand and officials remain confident cases will be caught at the border by the quarantine system.
The threat posed by the new omicron variant did not change plans for the reopening, after New Zealand on Sunday restricted travel from nine southern African countries.
Ardern said that New Zealand would move into a new pandemic 'traffic light' system based around the use of vaccine passports from late December 2.
Some attendees carried "Trump 2020" flags, while others bore signs carrying messages from Maori groups, those impacted by lockdowns, and teachers who face losing their jobs if they refuse vaccination.
Auckland has been in lockdown for almost three months after an outbreak of the delta variant.
The nation has been battling an outbreak of the delta variant of the coronavirus since last month.
Although beaten 6-4, 7-6 Julia Goerges in the Auckland final, Wozniacki said her preparation for Melbourne was on track.
Julia Goerges stunned top seed Caroline Wozniacki with a straight sets win in the WTA Auckland Classic final on Sunday.
Organisers said Caroline Wozniacki and Ana Ivanovic will compete at the Auckland Classic in January.