Raw sewerage emptied into the city's stormwater system near Parliament is now being investigated by Greater Wellington Regional council.

It comes after a handful of protesters were arrested this morning following a pre-dawn police operation, which installed barricades to encircle the occupation, now in its 14th day.

Reporters on the scene this morning described protesters climbing on trucks to stop the barricade, abusing passers-by, removing the masks of officers and even throwing human waste at police.

A warning has been issued by Land Air Water Aotearoa (LAWA), saying waste was being discharged into the western side of the harbour, affecting Taranaki St dive platform and the waterfront area around Shed 6.

"We advise people to avoid swimming, recreating, fishing in the harbour until notified", the notice said.

Council is also aware of reports that protesters are putting waste, including from portaloos, directly into street drains.

A council spokesperson said they were working closely with iwi, police, Ministry of Health, Wellington City Council, Wellington Water and LAWA.

"We will continue to monitor this situation but are unlikely to send our environmental monitoring team into the Parliament precinct to investigate to protect the health and safety of our staff."

It comes as a defiant Prime Minister Jacinda Ardern this morning renewed her message that it's time for the protesters to go home, doubling down on her refusal to meet with them or negotiate.

Around 3.30am police moved in and installed concrete barriers in eight locations, including Lambton Quay, Mulgrave St, Hill St, Molesworth St, Bunny St and Kate Sheppard Place.

The barriers are intended to prevent the protest at Parliament from expanding further into Wellington city and to maintain access for residents, businesses and emergency vehicles.

The concrete barriers, usually used for river works, are on loan from Greater Wellington Regional Council.

It's understood a select few protesters threw excrement sourced from portaloos at police officers during the action early this morning.

An officer told the Herald it occurred as officers held off protesters while concrete blocks were being put down at various streets around Parliament.

He also said some protesters ripped off police officers' masks as they clashed.

Later, police confirmed they were allowing sanitary vehicles through to clean protesters' portaloos. Earlier this morning, protesters claimed the vehicles hadn't been let through the barricades after they were set up at 3.30am.

A protester who woke to the surprise police action this morning described how protesters from all around the Parliament area were yelling and shouting as police moved in.

The man said many protesters were chanting "hold the line" as officers held off protesters while concrete blocks were placed at the end of various streets.

He said many of the children in the area were upset and crying as it was taking place.

On Featherston St protesters were seen climbing on to the trucks trying to stop the barricade.

Prime Minister Jacinda Ardern said she had been briefed this morning by Police commissioner Andrew Coster about the police operation.

The police are putting barricades around the perimeters and entry points of the protest to stop further growth and further disruption to Wellingtonians, she told RNZ.

She refused to budge on any of their demands, or consider meeting with them, saying the pandemic was top of her mind.

Speaking on TVNZ's Breakfast, Ardern said the measures that protesters are calling to be lifted and removed had helped to keep the country safe during the ongoing Covid pandemic.

Another record number of cases reported yesterday showed how real the situation is, she said.

"That is top of my mind - focusing on the pandemic.

"Now is not the time to pull down our armour and nor will we do it because people are camping on the front lawn."

She said it was not yet known what would happen if the protesters did not leave.

"What is very clear is that there is illegal activity happening here at Parliament," she said.

"People are being disrupted ... is not okay. They need to leave."

Meanwhile Wellington mayor Andy Foster said he had spoken with some protesters, and said the government needed to "at least" listen to them.

"Most people are perfectly reasonable to talk to and they told me their stories. I think it's useful to know that," he told TVNZ's Breakfast Show.

Foster acknowledged he wanted to see the situation solved without anyone getting hurt.

"We want to get our city back."

Commuters are being told to expect road closures around Parliament and to consider alternative travel routes, while the police traffic management operation is under way.

The railway station is still open and pedestrian foot traffic is not affected.

Police are also increasing their patrols around the schools and train stations, especially before and after school.

One Wellington school has told parents it will be practising its lockdown procedures so children know what to do if there is a physical threat in the school such as a "swarm of bees or an angry dog".

"We practise this in a way they feel comfortable and confident when they hear the special alarm," the school note said.