Wellington. New Zealand anti-vaccination demonstrators set alight their own protest camp outside parliament Wednesday after riot police moved to end their weeks-long occupation of the legislative precinct.

Ending a previous light-touch approach, hundreds of officers used perspex shields and pepper spray to force back protesters, who responded by pelting them with chairs, bottles and paint bombs.

When it became apparent that police were winning the battle for control of the makeshift tent city that sprang up on parliament's lawns three weeks ago, the demonstrators torched it themselves.

"This is not over," one man yelled, while others chanted "Shame on you" at advancing officers as a thick pall of black smoke enveloped the area.

Police deployed an ear-splitting sonic cannon to help disperse the crowd and made dozens of arrests in an operation that began just before dawn.

Speaking to reporters in parliament after initial skirmishes took place just a few hundred metres (yards) away, Prime Minister Jacinda Ardern backed the force's tough tactics.

She said what began as a movement against coronavirus vaccine mandates -- inspired by similar protests in Canada -- had turned toxic, describing demonstrators' conduct as "disgraceful".

"The protest has been at times violent. Increasingly we find misinformation and sadly conspiracy theories," she said, also labelling the camp a health risk for Wellington residents.

"It has become a location of interest, we know Covid has circulated within the protest and there have been hospitalisations as a result."

'It needs to end'

Police spent the morning clearing roads around the legislature, using a large forklift truck to remove cars and campervans that arrived in the capital in a convoy on February 8 and were used to jam downtown streets.

In the afternoon, they turned to the protest's epicentre on the lawns of parliament, where around 3,000 people congregated at the height of the demonstration about two weeks ago.

Numbers have since dwindled to a hard core of about 300 and police commissioner Andrew Coster said they had shown a willingness to use violence.

"We've seen tactics (from protesters) today including spraying fire extinguishers at the police line, the throwing of paint, early on we saw weapons," he said.

He said police were not seeking confrontation but added: "This protest has now tipped over a balance and it now needs to end."

At least three officers received minor injuries in the operation to clear the parliamentary precinct, which left a few dozen angry protesters milling on nearby streets yelling insults.

The operation came after vocal criticism from Wellington locals about the hands-off approach previously adopted towards the demonstrators.

Residents have complained about being abused by protesters for wearing masks, while schools and businesses close to the camp have closed for safety reasons.

In recent weeks, police have accused protesters of hurling human faeces at them, spraying a "stinging substance" at officers and slashing tyres on police cars.

Parliamentary officials initially tried to clear the grounds by playing pop music and children's song "Baby Shark" on a loop, but stopped after police criticised the tactic.

Coster said efforts to "de-escalate" the situation and end the protest without resorting to force had stalled.

"We reached the stage where protest leaders were unwilling or unable to effect meaningful change," he said.