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 was "unprecedented" for New Zealand.
"We've never had an occupation of this scale, certainly with tents on Parliament's grounds so ... some degree of uncharted 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."
About 4.30pm today, the crowd cheered loudly as police moved back from the line they had held for several hours, allowing the protesters to swell forward.
"Thank you! Thank you! Thank you!" protesters cheered, signalling a peaceful contrast to confrontations earlier today.
Police this morning said it was disappointing that despite the grounds being officially closed to the public earlier today, a number of protesters were refusing repeated requests to leave the precinct.
"We continue to acknowledge people's rights to protest, however those who behave unlawfully will face arrest."
Some protesters have responded with abuse, haka and hurling objects at officers.
A police officer was escorted inside Parliament in a distressed state after allegedly being sprayed in the face with an unknown substance by protesters.
Newstalk ZB's political editor Barry Soper confirmed he saw the officer being taken into the building by colleagues and that he "didn't look too well".
It comes as police crackdown on protesters who have been camped on Parliament's lawn in Wellington since Tuesday.
A heavy line of police has been gradually moving into the protesting crowd in a series of scuffles, with protesters taken away in handcuffs throughout the day.
Police were also beginning to remove tents erected by protesters and were moving into the crowd from both sides of Parliament's lawn.
Protesters are throwing water at police who are moving through the crowd and picking people out one by one.
Officers attempted to take down one of the group's marquees but were thwarted, to cheers from the protesters. However, in another section of the frontline, several more people were arrested and taken away in handcuffs.
Protesters can be heard screaming at the police, telling them "the world is watching" and that they are "a disgrace to the badge".
Some are describing the police response as akin to using " a nuclear bomb for a flea".
Multiple protesters are claiming to have been pepper-sprayed - The New Zealand Herald has sought confirmation of this claim from police.
Police earlier trespassed all protesters from the front lawn of Parliament, moving in to evict people as dozens of arrests were made.
Hundreds of protesters travelled to Wellington from across New Zealand on Sunday in a protest dubbed Convoy 2022 and have camped out on the grounds since.
The Speaker of the House, Trevor Mallard, closed the grounds in response to the anti-mandate protesters and the police presence has swelled dramatically.
Officers were taking a much tougher line with protesters, leading to about 50 arrests today.
"While Police acknowledges people’s right to protest, this needs to be conducted in a way that do not unfairly impact on the wider public," Superintendent Corrie Parnell, Wellington District Commander said this morning.
He said police continue to appeal to protestors to leave Parliament grounds peacefully, as the area is now closed to the public.
"It is disappointing that despite the grounds being officially closed to the public earlier today, a number of protesters are refusing repeated requests to leave the precinct. Police continue to take a measured approach, exercising their powers fairly and proportionately.
"We continue to acknowledge people’s rights to protest, however those who behave unlawfully will face arrest."
Supt Parnell said police had arrested more than 50 people, who face charges including trespass and obstruction, and will be bailed to appear in court. They will also be formally served trespass notices from Parliament Grounds.
He appealed to the owners or drivers of vehicles unlawfully blocking streets surrounding Parliament grounds to remove them immediately, or face enforcement action.
"Wellingtonians have the right to conduct their lives and go about their business without the interference of ongoing unlawful activity. Additional resources will be deployed from around the country as long as is necessary to ensure public safety."
Wellington City Council parking wardens will get a police escort to issue infringement notices to anti-mandate protesters' vehicles.
More than 100 additional police staff were called in, including from other districts, to assist today's operation and people were warned to avoid the area as the unrest could cause traffic disruption.
Earlier, at least two vans packed full of officers arrived at Parliament, forming a line as anti-mandate protests entered a third day.
Police began making arrests and shouted through a megaphone that protesters were trespassing: "Please leave now."
A female protester using a megaphone yelled: "They say we are doing something wrong. We are doing nothing wrong."
Some taking part in the protest are continuing to call for peaceful action. "We do not need any aggression or anger here".
Three arrests were made yesterday.
Prime Minister Jacinda Ardern said the evictions were a decision for police, and though every New Zealander had a right to protest, there were also rule about what happened on Parliament's forecourt.
"We would expect people to have behaviours that wouldn't disrupt others," she told reporters this morning and described the protest as "certainly not the largest I've seen".
Mallard said he wanted to see the protesters' tents gone.
"I would have liked to see them not there in the first place on Tuesday."
He did not wish to comment on the impact the protest was having on Parliament until after it was over.
Clogging main roads throughout the country on their way, the protesters had planned to stay in the capital and block the central streets there until their "demands" were met. Some threatened to enter Parliament.
Mayor Andy Foster said protesters had made their point, but had overstayed their welcome.
He stressed police were in charge of handling the protest and acknowledged it was "obviously a problem for our city" and affected people's ability to get around.
Local businesses were also affected, Foster told Newstalk ZB's Mike Hosking this morning.
"Marching in there issuing a few tickets doesn't move vehicles and clearly I think you can see the volatile situation we'd end up with our staff being putting themselves in danger.
"You've got a lot of people down there and they've (police) got to work out safely how this can be resolved and to make sure it's done without unnecessary people getting hurt.
"It has to be very well-planned and executed whatever you did."
Foster said the protest was causing major disruptions for businesses and for people getting around the city.
"I don't think we've seen anything remotely like this. From my perspective the protesters have made their point."
Wellington Chamber of Commerce chief executive Simon Arcus said Foster's comment today that the council did not have control of that part of the city "just isn't delivering what business needs".
"This is having a serious impact for businesses around the Parliament and across Wellington - additional pressure especially for our many hospitality and retail businesses, who are already making tough decisions facing a downturn at the red traffic light level, with this adding to further lost revenue and unrecoverable costs," he said.
"People are staying away from the CBD due to the protests, businesses are having to close for safety, and we've seen people being stopped from getting onto public transport to get home safely."
- additional reporting RNZ
