Police in riot gear have cleared the main protest hub in downtown Ottawa, using batons and pepper spray and making dozens of arrests, as they worked to flush out a hard core of demonstrators occupying the Canadian capital.

In a day-long show of force, hundreds of officers pushed into the city center, facing off in tense scenes with determined protesters who hurled gas canisters and smoke grenades at advancing police, linking arms and chanting "freedom".

By the afternoon, police backed by tactical vehicles and overwatched by snipers had cleared Wellington Street in front of the Canadian parliament – the epicenter of the trucker-led demonstrations which began almost a month ago over Covid-19 health rules.

Trucks were towed and tents, food stands and other structures set up by the demonstrators were torn down.

Ottawa interim police chief Steve Bell told a news conference "very important progress" had been made on day two of the operation to clear the protesters, though he cautioned it was "not over."

On side streets around the parliament, a police message boomed by loudspeaker told the few hundred die-hard demonstrators, "You must leave, (or) you will be arrested."

Mr Bell said 170 people had been arrested since the start of the operation, 47 of them on today.

As tensions increased, police used what they called a "chemical irritant" against protesters, who they said were being "assaultive and aggressive," launching gas canisters at officers.

Organisers of the so-called "Freedom Convoy" meanwhile accused police of beating and trampling demonstrators, urging their supporters in a statement to "move from Parliament Hill to avoid further brutality."

A protester kneels in front of Ottawa police before being arrested

Some truckers had chosen to depart on their own as the police closed in, driving away after weeks of demonstrations that at their peak drew 15,000 to the capital.

One of them was Vince Green, who said he and his wife, a former nurse who lost her job for refusing a mandatory Covid jab, had to return home to check on their kids.

Others remained defiant.

"I'm not leaving," Johnny Rowe told AFP, adding that there is "nothing to go back to".

"Everybody here, myself included, has had their lives destroyed by what's happened in the past two years."

Within minutes of deploying on Saturday morning, police had claimed a section of road in front of the prime minister's office.

Officers pointed guns as they smashed truck windows and ordered occupants out, with smoke filling the air.

As the operation unfolded outside parliament, lawmakers inside resumed debating Prime Minister Justin Trudeau's controversial use of emergency powers to subdue the protests.

The Ottawa police operation was the largest ever seen in the capital, drawing hundreds of officers from across the nation.

Mr Bell said police had opened several criminal investigations "that relate to the seizure of weapons".

And he warned participants in the protests that authorities "will actively look to identify you and follow up with financial sanctions and criminal charges".

Police smashed truck windows to make arrests

The Canadian trucker convoy began as a protest against mandatory Covid-19 vaccines to cross the US border. Its demands grew, however, to include an end to all pandemic rules and, for many, a wider anti-establishment agenda.

At its peak, the movement also included blockades of US-Canada border crossings, including a key trade route across a bridge between Ontario and Detroit, Michigan – all of which have since been lifted after costing the economy billions of dollars, according to the government.

Criticised for failing to act decisively on the protests, Mr Trudeau this week invoked the Emergencies Act, which gives the government sweeping powers to deal with a major crisis.

It's only the second time such powers have been invoked in peacetime, and lawmakers have split over their use.

Mr Trudeau said the act was not being used to call in the military against the protesters and denied restricting freedom of expression.

The objective was simply to "deal with the current threat and to get the situation fully under control," he said.

"Illegal blockades and occupations are not peaceful protests."