Declaring ‘zero tolerance,’ the police cleared the blockade at a vital Canadian-U.S. crossing.

The Canadian police in Windsor, Ontario, began making arrests on Sunday morning near the Ambassador Bridge, clearing a roadway to a vital border crossing to the United States and one of the most visible sites of an anti-government protest movement that has roiled Canada for weeks.

For the moment, the bridge remained closed, but the authorities suggested that might soon change.

“Today, our national economic crisis at the Ambassador bridge came to an end,” the mayor of Windsor, Drew Dilkens, said on Sunday. “Border crossings will reopen when it is safe to do so and I defer to police and border agencies to make that determination.

Earlier in the day, hundreds of uniformed police officers approached the protesters, some of whom had left their vehicles parked at intersections leading to the bridge. A phalanx of police officers warned the protesters they would be charged with criminal mischief, before closing in the small crowd and making arrests. A tow truck was used to removed a pair of parked pickup trucks blocking the approach to the bridge.

“There will be zero tolerance for illegal activity,” the Windsor Police warned in a statement.

The authorities also urged members of the public to avoid the area — but at least some appeared to have other ideas. On Sunday, a Facebook group supporting the protesters issued “urgent announcements” calling on people to make their way to the bridge.

In ordinary times, the bridge, which spans the Detroit River, is a main avenue of international commerce, with goods moving steadily between the United States and Canada. The nearly weeklong blockade has cost American automakers, in particular, millions of dollars.

In a meeting with senior officials on Saturday, Prime Minister Justin Trudeau “stressed that border crossings cannot, and will not, remain closed, and that all options remain on the table,” according to a government statement.

Mayor Dilkens, too, said Sunday that some lines could not be crossed.

“Canada is nation that believes in the right to freedom of speech and expression,” he said, “but we are also bound by the rule of law.”

On Sunday, the police defended their patient approach.

“Police used discretion during the course of the demonstration to avoid creating an unstable situation and potentially putting the public at risk,” they said. “This exercising of police discretion should not be confused with lack of enforcement.”

Catherine Porter and Vjosa Isai contributed reporting.