OTTAWA—Hundreds of heavy trucks and other vehicles continued to clog the streets of Canada’s capital city on Tuesday after Prime Minister Justin Trudeau announced the government’s plan to invoke extraordinary emergency powers aimed at forcing protesters to leave.

Mr. Trudeau said Monday his government would invoke rarely used emergency powers to shut down the encampment in Ottawa, which is now in its third week, and to deal with other blockades protesting Covid-19 mandates that have disrupted trade between the U.S. and Canada....

OTTAWA—Hundreds of heavy trucks and other vehicles continued to clog the streets of Canada’s capital city on Tuesday after Prime Minister Justin Trudeau announced the government’s plan to invoke extraordinary emergency powers aimed at forcing protesters to leave.

Mr. Trudeau said Monday his government would invoke rarely used emergency powers to shut down the encampment in Ottawa, which is now in its third week, and to deal with other blockades protesting Covid-19 mandates that have disrupted trade between the U.S. and Canada. While he has yet to detail how, specifically, those powers will be used, the so-called Emergencies Act would allow authorities to designate no-protest zones in areas near the border and to commandeer tow trucks to help them remove demonstrators’ vehicles.

Tamara Lich, a spokeswoman for the Ottawa protesters, operating under the Freedom Convoy 2022 banner, said the government’s plan was unlikely to dent demonstrators’ resolve. Ms. Lich and other protesters say they won’t move until Canadian governments’ drop all Covid-19 vaccine mandates and related restrictions.

“We will hold the line. There are no threats that will frighten us,” Ms. Lich said at a news conference.

Prime Minister Justin Trudeau’s decision to invoke the Emergencies Act was criticized by civil liberty groups, policy analysts and some political leaders.

Photo: dave chan/Agence France-Presse/Getty Images

The vehicles, among them heavy-duty trucks, have been parked on major downtown Ottawa streets for 19 days and counting, with a crowd of supporters swelling into the thousands for three straight weekends. The area around the country’s legislature has at times resembled a block party complete with a DJ, dancing, food service and fireworks. Residents have complained of excessive noise, including honking horns, and difficulty accessing their homes and completing basic errands like grocery shopping.

Security experts said they didn’t expect the protesters to be removed immediately, despite the additional powers announced by the government on Monday. Law-enforcement officials “will have to take some time to marshal the necessary resources and figure out how best to move against the protest,” said Wesley Wark, a senior fellow with the Center for International Governance Innovation, a think tank in Waterloo, Ontario.

Mr. Wark also rejected the notion, raised by civil rights organizations and some lawyers, that the government’s plan was too far-reaching for the circumstances. “This is not martial law,” he said. “This is a surgical instrument to give police at the local level certain tools.”

Canadian Minister of Public Safety Marco Mendicino said, ‘When we find ourselves in extraordinary times, we have to take extraordinary measures.’

Photo: BLAIR GABLE/REUTERS

Canada’s public safety minister, Marco Mendicino, said the emergency measures would allow the government to designate targeted zones adjacent to the border and prohibit assembly in those locations. “If you’re in that zone, then you can be charged under the Emergencies Act,” he said in an interview. “That doesn’t exist right now.” He said the government expected to choose targeted areas around some border crossings, rather than applying the rules to the entire U.S.-Canada border.

Mr. Mendicino said the government also wants to ensure that authorities can obtain tow trucks and concrete barriers where needed, to help remove vehicles the protesters have parked in Ottawa and elsewhere and keep people out of specific zones.

Security experts said the invocation also means the Royal Canadian Mounted Police will have a bigger role in managing the Ottawa protest. They added that the RCMP, in conjunction with Ottawa police, will likely need time to confer before deciding when and how to end the protest.

A key U.S.-Canada trade corridor has reopened for travelers and freight, marking an end to protests over Covid-19 restrictions that lasted roughly a week and caused economic repercussions. Photo: Nicole Osborne/Associated Press The Wall Street Journal Interactive Edition

Mr. Trudeau’s decision to invoke the Emergencies Act was criticized by civil liberty groups, policy analysts and some political leaders, who said they believe the protests and blockades don’t justify its use. The legislation is meant to confer extraordinary powers to the national government in the case of an emergency that threatens either public health, safety, sovereignty or national security, and the federal government judges these threats cannot be dealt with using existing laws.

Mr. Mendicino said the new emergency measures the government uses must be compliant with Canada’s Charter of Rights and Freedoms, which came into force in 1982 and protects rights considered essential to preserving a free and democratic society. The government has yet to inform parliament how the measures will be deployed, and its plan is subject to a vote in the legislature and upper chamber within seven days. Mr. Mendicino said the government expected to provide further details as early as Tuesday.

“When we find ourselves in extraordinary times, we have to take extraordinary measures,” Mr. Mendicino said.

The executive director of the Canadian Civil Liberties Association, Noa Mendelsohn Aviv, said the legislation the government is availing itself of is meant to deal with extreme emergencies that pose a risk to the security, sovereignty and territorial integrity of Canada. While the protests have been highly disruptive, she said, “we have laws and tools that were passed by democratically elected representatives to deal with them.”

Aaron Wudrick,

director of the domestic-policy program at the Macdonald-Laurier Institute, said the prime minister is deploying a “nuclear option” to deal with what is largely a downtown Ottawa problem—namely, getting tow trucks to remove vehicles. A senior city of Ottawa official said last week that tow-truck companies the municipality have on retainer have refused to remove the trucks in downtown Ottawa, due to worries about losing business once the protest ends.

Mr. Wudrick, a former lawyer, said police in Windsor were successful this past weekend in removing protesters who blocked cross-border traffic on the Ambassador Bridge, which connects Detroit with Windsor, Ontario, without the need for emergency powers. A Canadian court issued an order, at the request of the city of Windsor, granting police permission to remove the protesters, who disrupted U.S.-Canada trade for nearly a week.

“It’s more a logistical challenge than a threat to the integrity of the country,” Mr. Wudrick said. He added that he is worried civil liberties will be compromised, especially if tow-truck operators are forced to help police. “It seems to me that compelling individuals against their will to help the government seems like a suspension of civil liberties.”

Ottawa Police Chief Peter Sloly said this month his force of 1,200 officers didn’t have the resources to deal with the downtown protest, and Mayor Jim Watson has asked the federal government for an additional 1,800 officers to quell the demonstration. A representative for Ottawa police didn’t respond to a request seeking comment about how the use of the Emergencies Act might help end the protest. A spokesperson for the Royal Canadian Mounted Police didn’t respond to a request for comment.

The area around Canada’s parliament buildings has at times resembled a block party complete with a DJ, dancing, food service and fireworks.

Photo: ed jones/Agence France-Presse/Getty Images

Write to Kim Mackrael at kim.mackrael@wsj.com and Paul Vieira at paul.vieira@wsj.com