Canadian police have pushed into crowds of demonstrators to clear them from the streets of downtown Ottawa, arresting 70 and hauling away vehicles that have been blocking the core of the capital for more than three weeks in a protest against pandemic restrictions.

Fearing escalation or violence, Ottawa police had sought to disperse them with fines and threats of possible arrest, but on Friday hundreds of officers moved in despite the frigid temperature and freshly fallen snow, slowly clearing one part of the city.

Dozens of trucks still occupy the downtown area, but there are fewer now due to several leaving when the arrests began.

Police have also arrested the three most prominent organisers, two on Thursday and one on Friday.

Protesters being starved out

"We will run this operation 24 hours a day until the residents and community have their entire city back," Steve Bell, Ottawa's interim police chief, told reporters.

Officers set up 100 roadblocks near the protest site to deny people access and starve them of food and fuel.

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Police said they towed away 21 vehicles on Friday.

Commenting on the arrest of its leaders, Freedom Convoy 2022, an umbrella group representing the protesters, said: "We will continue to hold the line. We refuse to bow to abuses of power. The world is watching, Canada."

After a night of heavy snow, protesters with shovels erected a chest-high snow bank on Wellington Street outside parliament and positioned themselves behind it as they waved Canadian flags and Freedom Convoy posters.

Police have been driving the protesters toward parliament, clearing territory along the way.

"If they want to arrest me, I'll put my hands out and they can twist-tie me up like everybody else here. We're going peaceful," said Mark, a protester from Nova Scotia who would not give his last name.

Protesters vow to stand their ground

The protesters initially wanted an end to cross-border COVID-19 vaccine mandates for truck drivers. However the blockade has gradually turned into an anti-government and anti-Justin Trudeau demonstration.

The demonstrators have vowed to remain peaceful but say they will stand their ground until police physically remove them.

On Friday some protesters were dragged from their vehicles. Others who resisted the police advance were thrown to the ground and handcuffed.

While mostly non-violent, protesters did shout and push against the police line, and there were brief scuffles.

Video shared by Canadian media showed a young girl at the centre of a tightly packed group of protesters facing off with dozens of officers.

"Protesters have put children between police operations and the unlawful protest site," Ottawa Police said on Twitter.

"The children will be brought to a place of safety."

Emily McAuley, a teenage girl who was at the protest with her father and 12-year-old twin siblings, said she had come to "show some support" for the truckers.

She is from a town 30 hours away from Ottawa by car.

"Thank all you guys for fighting for mine and my brother and sister's freedom," she said.

Police say clearing the protests could take days.

At least one military-style armoured vehicle was seen in downtown Ottawa, and there were at least eight officers on horses.

Some police carried guns, and others had what looked like tear gas launchers. No tear gas was used on Friday.

'Stay away from downtown Ottawa'

The Prime Minister on Monday invoked emergency powers to give his government wider authority to stop the protests.

Legislators had been due to debate those temporary powers on Friday but the House of Commons suspended its session, citing police activity.

"If you are not in the House of Commons precinct, stay away from the downtown core until further notice," a House of Commons notice said.

Mr Trudeau sought the special powers after protesters shut down US border crossings including Ontario's Ambassador Bridge to Detroit, a choke point for the region's car makers.

The shutdown of the bridge, which was cleared on Sunday, had damaged both countries' economies and posed a major crisis for Mr Trudeau.

As police accelerated work to clear the protesters' last stronghold, at least a dozen tow trucks were working to remove trucks and other protest vehicles still parked downtown.

Many of the tow trucks had all identification marks removed.

Before Mr Trudeau invoked the emergencies act, police had said some tow truck drivers were afraid to cooperate with authorities, fearing they might be the target of retaliation.

Chrystia Freeland, Canada's Deputy Prime Minister, told reporters the protesters could not be allowed to undermine the government's authority.

"These illegal blockades and occupations will end, and they will end for good," Ms Freeland said.

Reuters