The unrest on Wednesday night followed the Quebec government's announcement it would suspend the current academic session for striking students in an effort to calm things down.
It also hinted at more punitive measures, without sharing details.
Sticking to his planned tuition hikes, Premier Jean Charest said he would table emergency legislation aimed at ending three months of disorder that has occasionally made international headlines.
The magnitude of the challenge was underscored by the fact that his announcement was instantly followed by raucous protests and warnings of potential violence.
In that charged atmosphere, thousands of chanting students spilled into the streets of Montreal, marching straight to the city's main commercial district. Their demonstration was peaceful until some rocks apparently thrown at police resulted in riot squad charges to clear Ste-Catherine Street.
As the mob was moved into other streets, nearby bank windows were smashed and objects were hurled at police. There was also a scuffle when an angry passerbys reportedly started heckling the protesters and crowded around him before police stepped in to split them up.
Once again, the acrid scent of police crowd-control chemicals billowed in the cool nocturnal air. This on a night when Charest shared plans to clean things up.
Authorities reported 122 arrests, three injured police officers and also some injured protesters.
Charest's legislation would temporarily halt the spring semester for the minority of faculties paralyzed by the walkouts; push up the summer holidays; and reconvene students in August so they can complete their session before starting the fall one in October.
The government also hinted at severe penalties for anyone who tries to picket or otherwise prevent students from entering classrooms.
Charest did not answer when asked about reports of stiff fines. He simply said those details would be revealed when the legislation is tabled — perhaps as early as Thursday.
He did make it clear the legislation will target the crowds of protesters who have blocked access to schools and even stormed into classrooms in an attempt to enforce what they call a legal strike.
"It's time for calm to be restored," Charest said Wednesday at a podium, flanked by several rectors and university-association officials.
"Access to education is a right. Nobody can pretend to defend access to education and then block the doors of a CEGEP or university.
"The current situation has lasted too long... Quebecers have a right to live in security."
Polls suggest Charest's unpopular government, facing a long-shot re-election bid, might actually have public support for its tuition hikes. But the premier has responded angrily in recent weeks when accused of encouraging a climate of confrontation for his own political benefit.
Bracing for more of that criticism, the Charest government has bought ads in Thursday's newspapers explaining how it has already made several adjustments to its tuition plans to soften the impact on the poorest students.
The ads emphasize another point Charest is keen for people to understand: 70 per cent of Quebec students have quietly finished their semester and aren't boycotting classes.
But the remaining legions of dissent won't easily be quelled and there were whispers of worse trouble to come.
"If there is violence, if there are serious injuries, Premier Jean Charest will have to carry the blame for the rest of his political career," said a visibly furious Leo Bureau-Blouin, who had gained a reputation in recent months as perhaps the most composed and moderate student leader.
Seated next to him, Martine Desjardins said: "If Jean Charest wanted to reduce tensions with this proposal, I'm really afraid that it will increase them instead... Young people will remember."
The tumult in Quebec has repeatedly made international news. It happened again Wednesday morning. Foreign media picked up reports about groups of protesters storming into Montreal university classes and forcing students to get out.
The three-month conflict has caused considerable damage — with numerous injuries, countless traffic jams, a few smashed windows, subway evacuations, clashes with law enforcement, a heavy police bill, and of course disruptions to the academic calendar.
The protests have even mushroomed beyond the cause of cheap tuition.
They have attracted a wide swath of other participants who dislike the Charest government and represent a variety of disparate causes — ranging from environmentalism, to Quebec independence, anti-capitalism and anarchy.
They have also prompted one of the most intense left-versus-right ideological clashes in recent Quebec history.
Such discussions have often taken a backseat in a province where the biggest debates since the 1960s have centred on independence, with political parties defined not by their differences on fiscal policy but by whether they're pro- or anti-sovereignty. Recently, political discussions have shifted onto things like the income-tax burden, the role of the state, and individual responsibility.
The dispute claimed the province's education minister, who announced her resignation from politics earlier this week. Her replacement, Michelle Courchesne, said Wednesday she'd noticed a hardening of demands from student leaders.
"There is no openness to make the necessary compromises," she said.
Her remark came as a surprise to the student groups, who had emerged from a meeting the previous night saying they'd had a constructive dialogue with her.
Parti Quebecois Leader Pauline Marois made it clear even before the announcement that she would oppose any legislated crackdown. Wearing the iconic red square of the protest movement, Marois said negotiation would always work better than coercion.
"I think the best way is to discuss," she said.
She picked up on an analogy used earlier in the day from a student leader. Bureau-Blouin had urged Charest to do the right thing as a "family father" — and deal with problems in the house, not call in the police.
Marois said that, speaking as a "family mother," she hoped for a peaceful resolution.
Quebec's bar association appeared to hold the same hope.
In a very nuanced, cautious statement, it called for mediated discussions between the students and government. It added that both parliamentarians and student leaders were democratically elected, the latter under provincial law governing student votes.
However, it also expressed concern over some protesters' disregard for the law. It called it "unacceptable" that legal injunctions, as well as the right to protest, appeared to have been ignored during occasionally violent clashes.
"For almost 14 weeks we've been watching growing social tensions and disruptions that are harmful to our social peace and legal democracy," the bar association said in a statement.
Opponents of the Charest government put their views far more tersely on Twitter.
"Charest (government) bringing in 'special law' to break student strike via stiff fines of picketers. It's time to rock n roll!" said Jaggi Singh, a well-known anarchist activist.
"Defying Charest's 'special law' is at heart a struggle for social justice, against capitalism & neo-liberalism." He said the "showdown is set" for next week, with a huge protest planned in Montreal.
Patrick Bourgeois, a hardcore pro-independence activist who recently quipped that this cause had turned him into a "revolutionary," was equally adamant.
"Now the system must be derailed," Bourgeois tweeted. "We will fight them intelligently, but we will fight them firmly, with courage!"
Under the latest version of its tuition plan, the Charest government would increase fees by $254 per year over seven years and then peg future increases to the level of inflation.
That would mean tuition increases of more than 75 per cent for Quebec students, who pay the lowest rates in Canada. The change would still mean some of the country's lowest rates.
But the antagonists in the dispute are casting this as much as a battle of principle as of public policy.
To the hike defenders, it's about improving the quality of universities, about students' personal responsibility, and about sparing Quebec's long-suffering taxpayers from an even heavier burden. To its opponents, it's about defending universal access to education against any future attempt to whittle it away.
Note to readers: This is a corrected story. An earlier version carried a typo in Martine Desjardins' name