Montreal police have arrested 36 people involved in a protest against the province's Plan Nord in the city's downtown core.

About 200 people rallied in front of the Palais des Congrès on Saturday where the Board of Trade of Metropolitan Montreal was hosting a natural resources networking event Saturday morning.

The Plan Nord — or "Northern Plan" — would touch on energy development, mining, infrastructure, tourism and conservation in a sweeping set of projects that, according to the government, would receive $80 billion in public and private investment over the next 25 years.

The peaceful demonstration, which ended midday, took a turn when some protesters tried to force their way into the building shortly after 9:30 a.m.

"We feel that officers have done a good job this morning. [They were] extremely patient," said Montreal police Sgt. Lafrenière.

"At 9:30 a.m. when people got to the Palais des Congrès with their crowbars, to break windows, then using a flare pistol to set a fire inside, we remove people. We disperse them."

He said no one was injured when the flare gun was shot.

Lafrenière said police decided to make arrests after four attempts to disperse the crowd.

Authorities deemed the protest illegal because organizers failed to give police an itinerary and because alleged criminal acts were taking place.

Sgt. Ian Lafrenière said 32 of the people arrested will be charged with taking part in an illegal assembly.

He said four people will be charged with assaulting police officers and for being in possession of stolen goods.

Plan Nord has been the subject of controversy since plans were unveiled by Jean Charest's Liberal government in 2011.

Police cars vandalized

On Friday, about 200 people gathered in Montreal's financial district to protest.

Police ordered the crowds to disperse early in the afternoon after at least three patrol cars were vandalized.

Montreal police Sgt. Laurent Gingras said protesters also sprayed graffiti and broke a window at the Palais des Congrès.