Thousands of protesters flooded downtown Montreal streets Thursday to protest what militant student group ASSÉ called "austerity measures" in the 2014 provincial budget.

Montreal police declared the protest illegal before it even began, around 2:15 p.m. ET, as students were still gathering in Parc Émilie-Gamelin near the intersection of Berri Street and Ste-Catherine Street East.

By the end of the protest, about three hours later, six people had been arrested for what Montreal police called "criminal acts."

Some protesters threw rocks, while police used tear gas, pepper spray, projectile launchers, batons and shields to push the crowds back.

A person in their 50s was injured after being hit in the head by a projectile, and a cyclist incurred a head injury when police advanced to disperse the crowd on Sherbrooke Street East.

Police said they did not use the kettling technique employed at many of the 2012 student protests to perform mass arrests, although they did have buses on hand as a precaution.

Student associations from primarily French-speaking CEGEPs and universities across Montreal and southern Quebec participated in the protest.

The protest is reminiscent of the 2012 student protests, sparked by the Liberals' attempt to increase tuition fees. During the six months of protests, thousands of people marched, hundreds of protesters were arrested and millions of dollars were spent on police overtime.

The outrage over increased tuition fees became a major election issue in 2012, with the Parti Québécois promising to stop the hikes if elected.

The PQ came to power as a minority government on Sept. 4, 2012.