OTTAWA (BLOOMBERG) - Prime Minister Justin Trudeau took a hard line against trucker protests that have paralysed Canada's capital city and have now halted commercial traffic to the United States at the busiest border crossing between the two countries.

The Ambassador Bridge that connects Windsor, Ontario, with Detroit was shut down in both directions late on Monday (Feb 7), according to a Canadian government website and the Michigan transportation department. It is the most important land crossing for goods between Canada and its largest trading partner and a crucial artery for auto parts suppliers and manufacturers.

About 1.4 million trucks entered the US through Detroit last year, almost all of them via the bridge, according to data from the US Department of Transportation and an association of bridge and tunnel operators. Protesters on tractors and trucks blocked access to another major US-Canada bridge about 100km north-east of Detroit on Sunday.

Mr Trudeau, speaking earlier on the floor of the legislature the first time since the crisis began, warned that demonstrators were hobbling the economy and trying to undermine democracy. He also dismissed contentions from the opposition Conservatives that the columns of big rigs parked along major thoroughfares in Ottawa are emblematic of a country bitterly divided over the pandemic.

"This is a story of a country that got through this pandemic by being united, and a few people shouting and waving swastikas does not define who Canadians are," Mr Trudeau said, referring to images from the initial days of the protest two weekends ago showing signs and flags adorned with Nazi symbols.

Mr Trudeau slammed the protesters for "trying to blockade our economy, our democracy and our fellow citizens' daily lives". He also raised his voice almost to a shout at one point.

"This pandemic has sucked for all Canadians," the prime minister said. "Everyone's tired of Covid-19, but these protests are not the way to get through it."

Horns muted

The Prime Minister's comments came hours after an Ontario Superior Court judge ordered a 10-day halt to deafening blasts from truck horns that have traumatised downtown residents.

The police have begun trying to cut off supplies to the trucker convoy, but have so far been unable to contain the demonstrations, prompting the city of Ottawa to declare a state of emergency.

The protesters, who have garnered global attention, say they will not leave until all Covid-19 health restrictions are dropped.

Disruptions to commercial traffic are a significant escalation for the protests, and risk igniting backlash that may aid Mr Trudeau. Other bridges between the two countries, including the Blue Water Bridge between Port Huron, Michigan, and Sarnia, Ontario, about 100km north of Detroit, remained open.

Mr Trudeau had largely been out of sight during the protest after testing positive for Covid-19 a week ago and going into isolation. On Friday, he said calling in the military was "not in the cards".

He had no appearances scheduled for Monday until just before the emergency debate, which was requested by the left-leaning New Democratic Party.

The Prime Minister said the demonstrators are effectively trying to overturn last September's election result, which saw his Liberals returned to power for a third term but without a parliamentary majority.

"We asked Canadians how they wanted to keep fighting this pandemic, and their answer was clear," Mr Trudeau said. "Canadians chose vaccines. They chose science."

Interim Conservative Leader Candice Bergen - who took the party's helm after Mr Erin O'Toole was ousted in a caucus putsch last week - challenged Mr Trudeau on whether he lit the fuse for the protest by demonising people who oppose vaccines and vaccine mandates.

"We are at a crisis point not only with what's going on out the doors and across the country, but the country overall," Ms Bergen said on Monday night. "And so much of it is because of the things that he has said and done."

But Mr Trudeau again insisted Canadians are united. He also praised the handful of Conservative lawmakers who have called for the protesters to leave Ottawa's streets, while imploring others to follow suit.

"I've seen members of the opposition call for an end to the blockades," Mr Trudeau said. "I salute that. This is a time to put national interests ahead of partisan interests."

While the race for a permanent Conservative leader has not officially started, perceived front-runner Pierre Poilievre has already announced his candidacy.

The firebrand finance critic, who represents a district on Ottawa's southern outskirts, has fully embraced the protests and is using the slogan: "Truckers, not Trudeau."