Flaming Molotov cocktails were hurled and windows were smashed during demonstrations designed as an act of defiance Friday against a legal crackdown by the Quebec government on student protests.

By the end of the hours-long protest, police had arrested four people.

Through most of the night the thousands-strong crowd remained peaceful as it sought to make the case that a new provincial law setting limits on protest, which only comes into application Saturday, will fail to end months of student-led unrest.

The calm was shattered at a downtown intersection where at least one incendiary device was lobbed. The object sailed overhead, before crashing down into the street in front of police.

It erupted in flames and a puff of smoke. A Canadian Press photographer reported seeing at least two such objects thrown and there were other reports of multiple devices being tossed at that spot on the edge of Chinatown.

Police responded to being pelted with projectiles by firing rubber bullets, noise bombs and tear gas into the crowd, causing them to scatter, clutching scarves over their faces and clamping their hands over their noses. One person was arrested for assaulting an officer.

"Criminal acts were committed," the police said in its Twitter feed. "[The protest] has been declared illegal. We asked people to disperse immediately."

The protest had been peaceful over its first hour. After a tense few moments, it carried on that way and police let the march continue.

Police move in on protesters during a large demonstration designed as an act of defiance against a legal crackdown by the Quebec government. (Graham Hughes/Canadian Press) The cat-and-mouse game with police continued late into the night as another smaller demonstration snaked into the trendy Plateau area where the window of a bar and a bank branch were smashed.

Participants at the bigger demonstration had said they were encouraged by the strong turnout and by the support from bystanders.

While some motorists were miffed about being stuck in traffic jams, many honked their car horns while sidewalk observers clapped in a show of support.

Scores of gawkers rushed onto the street in the downtown commercial core to watch the protest and take pictures and the students marched defiantly past, a drummer's beat setting the tempo for their brisk stride.

While many onlookers yelled words of encouragement, not everyone was friendly. Some observers scowled as the students went past.

There were reports of one man getting his window smashed after flipping the protesters a single digit salute. A shopkeeper who told the students to quit causing trouble got a barrage of expletives.

Fireworks and firecrackers were set off at the corner of Mont-Royal Avenue and St-Laurent Boulevard, and in some spots protesters kicked and threw projectiles at police cars.

There were protests in different cities Friday and another demonstration started in Montreal as one ended.

"A protest, each day, until victory comes our way!" is one of the common chants, translated from French, at these nightly events, and it was frequently heard Friday in Montreal.

There have also been numerous, and in some cases physically threatening, chants about Premier Jean Charest.

Opponents of the Charest government – including its political opposition – have begun attacking its approach to the protests, evenmore than the tuition hikes that originally sparked the unrest.

The Parti Québécois, for instance, has played down talk about the fee hikes which may have strong support, according to some polls.

The sweeping legislation introduced, debated and passed over less than 24 hours is an entirely new political target.

The Montreal march came hours after the government passed Bill 78, which sets some limits on the ability to protest following weeks of unrest.

Also Friday, a new municipal bylaw imposed stiff fines on people wearing masks while demonstrating.

A few people in the crowd were in fact wearing masks. However, the mask bylaw and the protest limits were not being enforced before Saturday.

Police said they were given the march route in advance — one of the many stipulations of the new provincial law. They were not commenting, however, on reports that their phone lines were flooded by people calling to report the route, in a unique gesture of civil disobedience.

Montreal police said they didn't enforce Bill 78 on Friday night because they were still determining how it was to be applied.

Friday protest draws new supporters

Friday's nighttime protest was the 25th such demonstration but some participants said this was their first one.

Milly Pominville, a 20-year-old junior college student, acknowledged she was nervous attending the protest after the passage of the special law.

"I don't want anything bad to happen," she said. "But I hate Jean Charest so much. He has to go."

Pominville called the new law "stupid" and vowed to return for the marches every day from now on.

The nighttime protests have been going on every night for nearly a month — Friday's was the 25th in a row.