Police in Canada's capital gathered on Thursday to remove a trucker-led protest that has clogged Ottawa's streets and prompted the government to invoke rarely-used emergency powers.

Prime Minister Justin Trudeau was in Parliament nearby, justifying his decision to apply the Emergencies Act for only the second time in peacetime, with barricades being up overnight and a large police presence emerging in the region where hundreds of big rigs remain parked.

"Illegal blockades and occupations are not peaceful protests," Trudeau told the House of Commons, adding, "They have to stop."

In response to concerns, he stated that the Act was not being used to call in the military to suppress demonstrators and that the Act did not restrict freedom of expression. He stated that the goal was to "deal with the current threat and get the situation fully under control."

Police officers were spotted descending from buses and filing into the parliamentary precinct in Ottawa, where the trucks had been parked for weeks, on Thursday morning. 

The interim police chief of the capital city had ordered truckers until late Wednesday to "leave the area now," or face arrest and vehicle seizures.

Potential for 'terrorist attacks' 

Faced with mounting pressure to evict the demonstrators, Trudeau used unusual emergency powers this week to put a stop to the sit-ins that have been occupying Ottawa and, until recently, impeding border crossings to the United States.

Justin Trudeau told reporters Wednesday that with police getting help from various other law enforcement units, they should now "be able to begin their actions." "It's time for this to end," he said.

The government outlined its justification for using emergency powers in documents submitted with the House of Commons, claiming that the trucking convoy has created a serious and urgent situation that cannot be addressed under existing Canadian rules.

It cited "a risk of serious violence and the potential for lone actor attackers to conduct terrorist attacks."

In a letter to provincial premiers, Trudeau decried the protests as "a threat to our democracy", adding that, "it is affecting Canada's reputation internationally, hurting trade and commerce, and undermining confidence and trust in our institutions."

Trudeau: A threat to our economy 

On Monday, the Prime Minister used emergency powers to ease border blockades and clear the streets of Ottawa of truckers.

"The goal of all measures including financial measures in the emergencies act is to deal with the current threat and to get the situation fully under control," Trudeau said. "The blockades and occupations are illegal," he said.

"They're a threat to our economy and relationship with trading partners. They're a threat to supply chains and the availability of essential goods like food and medicine."