MONTREAL - A spring of discontent in Quebec characterized by images of red-clad student protesters took on a darker tone Friday as downtown streets were disrupted by scenes of increasingly intense civil unrest.

Demonstrators hurled projectiles from rocks to flower pots in Montreal, committing vandalism outdoors and interrupting different political events indoors. Some vandals even tossed rocks from an overpass onto a busy downtown expressway, police said.

Riot police fought back by swinging batons and firing rubber bullets into the crowd.

There were no reports of any injuries on the expressway, though at least six people were slightly hurt — including four police officers — in a long day of demonstrations.

Provincial police were called in as local officers struggled to handle crowds that disrupted two separate events, including one featuring Premier Jean Charest and, to a lesser extent, one involving federal Immigration Minister Jason Kenney.

There had already been warnings that some students saw their daily protests as more than a fight against tuition increases. Some had taken to referring to the demonstrations as Quebec's "Maple Spring," in a rhetorical nod to broader protest movements elsewhere in the world.

That point was repeatedly driven home Friday by protesters who signalled that the unrest was about more than university fees — it was about the general direction of the province.

"It's not just the tuition increase," said Alexis Remartini, 18, who took a 60-kilometre bus trip from St-Hyacinthe to attend the protest.

"The movement has grown to include other things we don't agree with."

Friday's most chaotic scene unfolded at a high-profile Charest event, as projectiles and tear gas rained on what was supposed to be the premier's political parade.

The symposium on the premier's signature northern-development plan was to have served, some pundits speculated, as a springboard into a provincial election. No vote date has been set.

Charest's lunchtime speech on his Plan Nord was delayed by 45 minutes after protesters managed to bust into the Palais des congres convention centre.

Protesters made it within a flight of stairs of where the luncheon was being held. They were met with a line of riot police, who eventually removed them from the building.

The premier made it clear he had no intention of backing down from his tuition hikes, or from his northern-development plans.

Charest even joked about the protesters during his speech: "Maybe those knocking on the door this morning, we can offer them jobs," he said, to laughter. "In the north, if possible."

Outside, there were scenes of virtual anarchy.

While some protesters hurled objects and built barricades in the street with construction materials they'd found, police fought them off — at one point firing chemical irritants right into one young man at nearly point-blank range.

Seventeen people were arrested as police announced over a loudspeaker that the protest was being declared an illegal assembly.

Demonstrators left a scene of destruction in their wake as they weaved through the downtown streets, backing up traffic. Garbage cans were overturned and trash strewn about. At least three police cars had their back window smashed, and a window at a main entrance to the convention centre was also broken.

Nicolas Moran, 21-year-old law student at the Universite du Quebec a Montreal, was one of the students who had earlier managed to get into the building.

He had a gash on his forehead and blood on his shirt.

"I wasn't doing anything violent," he said. "A police officer hit me over the head... But I doubt the education minister will denounce violence from police."

Well behind schedule, Charest finally began a speech that some had expected might serve as a precursor to an election, which the premier must call by late next year.

Charest earned a standing ovation as he walked on stage.

After thanking the crowd for its patience, the premier quickly slipped into his prepared text and described northern development as an inter-generational project deeply embedded in Quebecers' "DNA," sharing his own family history with the north.

He said the plan, which focuses on mining and energy production, would help create thousands of new jobs and "move Quebec forward."

Speaking with reporters afterward, Charest insisted he will not back down on $325-a-year tuition hikes that will raise fees 75 per cent over five years. Even with the increase, Quebec would still have among the lowest tuition rates in the country.

While police said Friday's worst vandalism was not necessarily tied to tuition protests and was possibly the work of other troublemakers, Charest stuck to a familiar script.

The premier focused his response to the events on his preferred political target: the most radical student protest group, whose acronym is C.L.A.S.S.E. Opinion polls have been unkind to the premier lately, but the latest surveys suggest there is some sympathy for his position on tuition fees.

Charest has been refusing to negotiate with the C.L.A.S.S.E. because the group has avoided taking a stance against violent forms of protest.

"The social disruption is unacceptable," Charest told reporters after his speech.

"I've had ministers' offices ransacked. We've had ministers who have had tanks of gas put on the grounds of their homes. Molotov cocktails in front of their offices. Death threats.

"And they refuse to condemn violence? In 2012, in Quebec? That's unacceptable."

Also looming in the backdrop are conflict-of-interest and ethics scandals dogging Charest's government.

His latest headache stems from an investigative report that a well-connected political organizer has been peddling cash-for-access schemes related to the Plan Nord.

Charest's goal is to develop a 1.2-million-square kilometre stretch of the province's north over the next 25 years. Charest has said it will create 500,000 jobs, though his claims have been met with skepticism from opponents who call the plan everything from a marketing gimmick to a sellout of Quebec's resources.

An investigative show on the French-language CBC showed a provincial Liberal organizer — and onetime prominent organizer for the Harper Tories — discussing the Plan Nord while being surreptitiously videotaped.

That organizer, Pierre Coulombe, was videotaped suggesting to reporters, who pretended to be potential clients, that they could have access to Plan Nord decision-makers for a fee.

Instead of handing cash-filled envelopes to political insiders, he suggested clients should simply promise them multi-year jobs on their departure from politics.

He indicated such jobs might pay them about $25,000 annually and require that they attend only one meeting a year while being sent on occasional business trips to Europe.

Not far from Charest's event, an announcement by the federal immigration minister was also interrupted by two protesters who had bought tickets to his speech.

As Kenney began his speech, they twice shouted that his immigration reforms would destroy people's lives. They were both quickly escorted out of the hotel room.

Kenney was in Montreal to announce, in his latest immigration policy reform, that people must prove they can speak English or French to gain Canadian citizenship.