Police have warned protesters occupying central Ottawa of “imminent” action to clear them from the capital and began making some arrests to end a crisis that Canadian Prime Minister Justin Trudeau warned was threatening public safety.

Truckers opposing coronavirus mandates have blocked roads in downtown Ottawa for nearly three weeks, the centerpiece of a movement that has inspired anti-government protests in other countries and temporarily shut border crossings with the United States.

Threats of fines and jail helped convince protesters to retreat this week from four US border points. Police have issued similar warnings in Ottawa, where interim Police Chief Steve Bell said they were committed to driving protesters out.

“We’ve been bolstering our resources, developing clear plans and preparing to take action. The action is imminent,” Bell told reporters. “To those engaged in the unlawful protests – if you want to leave under your own terms, now is the time to do it.”

Police were seen arresting several protesters on Thursday evening, including two of the main fundraisers and organisers, Chris Barber and Tamara Lich.

Officers handcuffed Barber and placed him in the back of a police vehicle, a video posted to the organizers’ Facebook page showed. Later they arrested Lich, a video on the organisers’ Twitter page showed.

The arrests marked an escalation of police activity that has drawn the defiance of protesters, who honked their horns in unison earlier on Thursday in violation of a court order. Others shrugged off the warnings and soaked in a portable hot tub set up near a door to parliament.

Police said they would restrict access to downtown Ottawa and that officers had begun erecting barriers around government buildings. They have also distributed leaflets warning truck drivers and others of “severe penalties”.

While officers have not physically removed people, the increased police presence has demonstrators bracing for action and urging one another to remain calm.

Some 400 vehicles are parked outside parliament and the prime minister’s office, paralysing downtown. Calling the blockades a threat to democracy, Trudeau invoked emergency measures on Monday giving his government temporary powers to clamp down.

“The blockades and occupations are illegal. They’re a threat to our economy, the relationship with trading partners, they’re a threat to supply chains and the availability of essential goods like food and medicine. They’re a threat to public safety,” Trudeau said on Thursday.

The demonstrators initially protested against cross-border COVID-19 vaccine mandates for truckers and other restrictions. But they have made clear their opposition to Trudeau and some say they want to see him forced from office.

Meanwhile, Trudeau recently brought in new emergency orders that has given his government the ability to freeze people’s bank accounts who are involved in the protests.

Get all the latest Canberra news, sport, entertainment, lifestyle, competitions and more delivered straight to your inbox with the Canberra Daily Daily Newsletter. Sign up here.