Police are warning it could take days to remove anti-mandate protesters from Parliament's lawn.
Speaking at Parliament, Wellington District Commander Superintendent Corrie Parnell said the occupation is "unprecedented" for New Zealand.
"We've never had an occupation of this scale, certainly with tents on Parliament's grounds so ... some degree of unchartered waters."
The police have moved to a "state of enforcement action" arresting 120 people today, he said.
They face charges of trespass or obstruction.
"We've continued to try and really encourage those persons present here to peacefully desist and effectively now have been trespassed from the grounds of Parliament. Despite our hope that they would do that willingly and peacefully, that hasn't come to fruition."
Two officers have been assaulted during the operation, Parnell added.
Officers have spotted weapons like placards, sticks and a knuckle duster which signalled the sentiment of some of the occupiers, he said.
Additional resources will be brought in from around the country in the coming days, he said.
"I've got 150 additional resources over and above my district resource of 900 staff and I'll continue to add to that, in the coming days."
Parnell anticipates it could be days before Parliament's lawn is cleared, but said he does not intend for the occupation to be there for another week.
"This was never going to be a short task ahead of us."
The police are "well advanced" with plans to remove the vehicles that are blocking streets in Wellington's city centre, Parnell said.
Vehicle owners have so far resisted requests to move the vehicles, he added.
An "absence of leadership" is making it difficult to negotiate with organisers, he said.
"There's so many different causes and groups here and to some degree, there is actually an absence of leadership.
"Yes, we have had good negotiations, certainly in the early stages, with organisers. And if you go back to the convoy ... when the people first arrived here, good open lines of communication but we've transitioned beyond that now."
Police are very concerned about the lack of masks and possible low vaccination rates of participants, Parnell said.
"The health and safety of our people and also the public is paramount. It's really clear that we're operating in a Covid environment."
Conditions for officers have been difficult, Parnell said, with rain this morning and working with masks on.
See how the day's events unfolded with RNZ's live blog: