Protests turned ugly Friday as students stormed a Montreal convention centre to interrupt a speech by Premier Jean Charest.

Montreal Police, backed up by Quebec's provincial police, turned back hundreds of student protesters who hurled rocks, traffic cones, garbage cans, and other objects at the lines of police officers.

The officers, who surged at the protesters in rows before backing off, retaliated with pepper spray and smoke bombs while a QPP helicopter hovered overhead.

At least a dozen protesters were arrested shortly before 2 p.m.

One police officer suffered a head injury, while a journalist was struck in the leg by a rock.

At the height of the protest, demonstrators smashed windows of Palais des congres, and damaged cars and media trucks.

Montreal police also reported that protesters were throwing rocks off the St. Laurent Blvd. overpass, striking cars on the Ville Marie Expressway.

Police later gained the upper hand by forcing them to splinter off into smaller, more manageable groups.

"It was an intense situation. You had riot police lining up on one street corner and you had more than 100 students actively engaging them in a fight. Really pushing them to come at them," said CTV News reporter Tarah Schwartz.

Students and environmentalists banded together to protest the Plan Nord, Charest's cherished political project to develop the province's north.

Charest has a 25-year plan to develop a 1.2-million-square kilometre stretch of the region. The premier says it will create some 500,000 jobs, but his claims have been met with skepticism as opponents see it as nothing more than a marketing gimmick and a sellout of Quebec's resources.

About 45 minutes behind schedule, Charest finally began a speech that, for months, some had expected might serve as a launching pad into an election campaign.

The first words out of his mouth were: "Thank you for your patience."

The premier then quickly slipped into his prepared text, and described northern development as an intergenerational project deeply embedded in Quebecers' "genes" and "DNA," sharing his own family history with the north.

Student groups who have been protesting tuition increases also say the Plan Nord is another example of a policy that doesn't reflect the values of Quebecers.

"It's not just the tuition increase," said Alexis Remartini, 18, who took the bus from St-Hyacinthe for the protest. "The movement has grown to include other things we don't agree with."

Still, student leaders say they have become frustrated by the lack of interest from the government that has not paid much attention to the students' concerns during the 10-week strike.

"The government is going to have to come to its senses. It is going to have to invite all three of the national movements to the table and they are going to have to discuss in a very practical way how to resolve this," Mathieu Murphy-Perron, an organizer for the Dawson College Student Union, told CTV News Channel.

Murphy-Perron also defended the extended actions of the students, but did not comment on the violence.

"The Quebec student union has a long history of using striking as a tactic to influence government policy. . . It has been a very, very useful tactic and probably the most efficient in North America."

Earlier in the week, the offices of several Quebec cabinet ministers were vandalized in Montreal in an hour-long vandalism.

Windows were smashed on Monday, Molotov cocktails were thrown and red paint was splashed on the offices. The city's underground Metro system was also targeted.

With files from The Canadian Press