They came in early this morning and they came in hard - and the police won't stop until the unlawful protest is over. 

And a former frontline cop says the best thing protesters can do is give up and go home. 

"My advice would be that they should go home now, it's gone on long enough and it's not a protest anymore - it's just people who want to be there and fight with police," he said. 

"The best thing they can do is go home - it's over. 

"These things can only be tolerated for so long." 

Early this morning police moved in to take back the grounds of Parliament from anti-vaccine and anti-mandate protesters who have been occupying the site for 23 days. 

More than 100 officers are on the ground moving through the protest and dismantling tents and structures. 

The pre-planned operation started at 6am and police said the aim was to "restore access" to Parliament. 

The former officer said the operation would have been a long time in the planning. 

It is understood specialist police from around the country - including Armed Offenders Squad teams - have travelled to the capital to assist. 

"They've obviously come up with a plan and logistics, which seems to me to get out and clear the protest out," he said. 

"Initially there was a core group of actual protesters but then they were joined by all the fringe radicals - people who just want a battle. It seems like the ones who are left are mostly the rabble. 

"It looks like what police are doing is taking out bits at a time and then moving everything and everyone out... I imagine their plan is to remove all the infrastructure from there today. 

"They will take it out piece by piece rather than coming at the protesters in one big group - section them off, split them up, sort them out and then move to the next." 

He said the tactic was a "divide and conquer" style. 

The former officer who spent decades in police suspected the "legitimate protesters" would head home today. 

"They don't want the battle with police, they want the protest.... it will just be those who want to fight and fight back left," he explained. 

As officers moved down streets protesters fought back - throwing objects, screaming abuse and confronting officers. 

Some have hurled full water bottles and discharged fire extinguishers at the police. 

One officer who was blasted in the face by the foam from the extinguisher was seen being treated by paramedics. 

Herald reporters in Wellington have seen protesters can be seen building buffers out of pallets to try and stave off police advances. 

According to one livestream from the grounds of the protest, some protesters are calling for children to be taken to the front of Parliament House to act as a buffer between them and the police. 

A number of people have been led away by police - and 20 formal arrests have been made. 

Police said officers had so far sighted protesters in possession of various weapons including homemade plywood shields and pitchforks. 

Protesters have also been pointing a laser at the police helicopter. 

Journalists are also being threatened - with one reporter and camera operator chased and told "we will hang you bro". 

The former officer said the level of weapons was a concern. 

"Any weapon has the potential for harm - pitchforks, anything like that could do a lot of damage," he said. 

"The police have got to be planning for that... they will bring in the AOS, not for their gun ability but because they have extra training in dealing with people and weapons. 

"There's always the potential for police to get hurt, and for other people to get hurt." 

He said police would also be planning for the presentation of firearms by disgruntled protesters. 

"There is obviously potential for that - they've got all sorts of weapons and things there," he told the Herald. 

"You cannot discount that there are firearms there, it's certainly possible and police would have to factor that in." 

So why today? Why did the police move this morning? 

The former cop said top brass including Commissioner Andrew Coster would have been planning the strategy, tactics and logistics for days if not weeks. 

"Then they have made the decision to go in today," he said. 

"I would think that this is at least going to go all day," he said. 

"And if they stop, people will just come back so they just need to carry on and get it done... depending on how much the protesters refuse to leave, this could go on for a long time though. 

"But from what I have seen, it doesn't look like the police are mucking around." 

Just before 9am police announced they had "gained significant ground this morning" in the operation "to restore lawful protest". 

"We continue to urge those wishing to leave to let our staff know," a police statement said. 

"We will work to facilitate their safe exit from the area. 

"Protesters have been reminded that Parliament grounds are closed, and that they are trespassing." 

A Herald staffer at the scene said: "Just seen about 20 children being led away from Parliament, protesters are packing up."