Prime Minister Jacinda Ardern says she is saddened and angered by the protesters' actions today, and that parliament's grounds have been desecrated.

Ardern has addressed media, after an afternoon that has seen fires lit, explosions and objects thrown at police as an anti-vaccine mandates protest sparks violent scenes.

There have been multiple arrests, vehicles have been towed away and some protesters have suffered injuries. Some set fire to protesters' tents arousing concern that gas canisters would explode, and some large blasts were heard.

Watch the media briefing here:

Police were able to take back much of the ground the protesters have been occupying for the past three weeks.

Ardern said she was angry and deeply saddened to see Parliament desecrated in the way seen today, including the children's playground being set alight.

She says it demonstrated why the government refused to engage with the group.

"It was an illegal occupation, they engaged in hostile, violent and aggressive behaviour throughout the occupation, and today that has culminated in the desecration of this Parliament's grounds. I am absolutely committed we will restore those grounds and we will not be defined by one act by a small group of people."

Asked about those who have been throwing projectiles at police, including LPG bottles thrown on flames and cobblestones hurled at officers, she said there were "words I cannot use in this environment for what I saw today".

She said while the events today did not surprise her - considering the anger protesters had already expressed in the past few days - Ardern said it did sadden her.

She said anyone still throwing projectiles should "put down their weapons long enough for police to arrest them".

Ardern said there was a place for peaceful protest in this country, but "this is not the way that we engage and protest". She said peaceful protest was the way to send a message, this by comparison is "a way to end up before the courts".

Asked if protesters will be able to return overnight or tomorrow, Ardern said police will be present at Parliament.

She said the commissioner wished to make the point that there will be a substantial police presence in Wellington, and locals should be assured that while this had been a distressing period, police will continue to make their presence felt and keep them safe.

Ardern said she knew that in planning for today's operation, police expected there would be "hostility, resistance and violence".

"They planned for that because that is what they and Wellingtonians have experienced for several weeks now."

She said while they planned for it, it was another thing entirely to witness it.

"To our frontline police and emergency and fire services, you have our deep admiration and our thanks. You have been calm but resolute in trying to bring this occupation to a conclusion. It has come at great risk to your personal safety. Thank you for putting others before yourselves."

She said she has spoken to the police commissioner and there have been various injuries sustained by officers, but she will leave it to him to go into more detail.

Ardern says the fires created in the front of Parliament, including at the war memorial are causing more distress than what the police would have done today.

She said she believed the force that was used was used to keep others safe.

She said police have been mindful of the presence of children throughout the occupation, and there were other agencies present should there be a situation where children were left unsupervised or uncared for, such as if parents were arrested.

Ardern said it was almost impossible to comprehend that people would stand opposed to efforts to slow down the spread of a disease, when it has infected 20,000 and put more than 400 in hospital in just one day.

She said while many have seen disinformation and dismissed it as conspiracy theory, a small portion has believed it and acted on it in a violent way.

"This cannot stand."

Ardern said this afternoon's events were an attack on frontline police, an attack on Parliament, and an attack on New Zealanders' values, and it was wrong.

"Our country will not be defined by the dismantling of an occupation. In fact when we look back on this period in our history, I hope we remember one thing. Thousands more lives were saved in the past two years by your actions as New Zealanders than were on that front lawn of Parliament today.

"The sacrifices we were all willing to make to look after one another, that is what will define us, no protest, no fire, no placards will ever change that. Today the police will restore order and tomorrow your government will work hard to get us safely back to the normality everyone deserves."

Ardern said there was nothing to suggest that security settings as a country needed to change in response to the protest. She said it was estimated there were about 270 protesters who were causing the acts of violence and destruction seen today.

"That demonstrates it only takes a relatively small group of people who are committed to destruction to cause it, should they so choose. But it also demonstrates it was not a large group who were engaging in those acts either.

"We are not going to dismiss some of the underlying causes of what we have seen, but nor will we excuse it."

She said work will be done to address how misinformation and disinformation led to what was seen today, but the government "will be at pains to ensure that it never becomes an excuse for the violent acts that it resulted in".

"It's a dangerous place when citizens are led into spaces where they believe so deeply in conspiracy theory that they react with such violence."

Ardern acknowledged there have been for a long time a group of New Zealanders who have been living on the margins and have subscribed to other conspiracy theories, and "this happens to be the current rallying cry".

Ardern says finding a solution to disinformation and misinformation is not about taking away people's ability to have differing opinions or debate, to take different positions.

"People should of course always have that freedom of thought and view and perspective and in New Zealand we've celebrated that, but when the debate you're having is no longer based on fact, where does that take you? That is the challenge we have."

RNZ