An early morning student demonstration in downtown Montreal ended with chemical irritant and protesters zigzagging through the streets.

About 250 protesters blocked the entrance at the CIBC tower at René Lévesque Boulevard and Peel Street before Montreal police declared the demonstration illegal.

According to Const. Daniel Fortier, the order to disperse was given at 8:40 a.m., but several protesters refused to comply. He said some of the demonstrators had committed mischief earlier in the morning while marching downtown.

He didn’t specify what the acts were.

Tactical officers moved in on the demonstrators at CIBC, pushing them back with shields and spraying chemical irritant to disperse the crowd.

The group retreated, running through the streets until the protest was finally declared over just before 9 a.m.

Some of the demonstrators threw rocks at buildings and knocked over garbage cans.

The demonstration, organized by student group AFESH-UQAM, started at Phillips Square at 7 a.m. The demonstration was labeled "Shutdown Centre Ville," on the group's website and described as a "mega demo."

Two groups split off, travelling on two different paths through downtown.

Montreal police report two people were arrested.