MONTREAL - A peaceful evening march that began with people banging pots and pans in support of protesting students ended in the early morning hours with police kettling demonstrators and arresting more than 506 in a group arrest after officers were pelted with projectiles.

Montreal police say they hope the public understands officers are trying to use discretion as they monitor, and in many cases break up, the protests that have occured on a daily basis in the city for the past 102 days.

Sergeant Ian Lafreniere said that when 518 people were detained on Wednesday evening police were not trying to break a record.

"But that having been said citizens of Montreal ask us to restore the peace, to bring back the Montreal they know," said Lafreniere.

The officer offered an apology for anyone who was detained during the kettling tactics, and admits it rounded up innocent bystanders.

"Yesterday we declared an illegal assembly at 8:30 and people [were] apprehended at midnight. So people who said it was impossible for them to leave, three and a half hours, even if you're not a fast walker, normally you should leave," said Lafreniere.

Police say that more than 1,500 people have been arrested or detained since the protests began, but Wednesday night was the first time anyone was detained for wearing a mask, in accordance with a new municipal bylaw.

According to police that individual was hiding his face to commit a criminal act.

Political reaction

In Quebec City Finance Minister Raymond Bachand was critical of a New York Times opinion piece written by a pair of University of Montreal teachers which asks people to stay away from Quebec this summer.

He also said protesters should stop hurting the city of Montreal.

"They are the right to express socially their disagreements with the government, but they should take into consideration that they should not take Montreal as hostage in that, because it is hurting the city, and it's collateral damage which is becoming very serious,' said Bachand.

The protest

Kettling is a police tactic widely used in Europe where riot cops surround demonstrators and limit or cut off their exits. It has been widely criticized because it often results in the scooping up of innocent bystanders as well as rowdies. A recent report by Ontario's police watchdog blasted Toronto police for their use of kettling during the G20 summit two years ago, saying they violated civil rights, detained people illegally and used excessive force.

The Montreal demonstration was the 30th since the student protest against tuition fee increases began more than three months ago.

The nightly march, which starts from an east-end park, was declared illegal by police the minute it was scheduled to start but was allowed to proceed for almost four hours before a line of Montreal riot cops blocked part of Sherbrooke Street as the marchers approached.

Riot squad officers had been marching on the sidewalk beside the front of the protest all evening. An order to disperse was given when it arrived at Sherbrooke Street because police had been pelted by projectiles and other criminal acts had been committed, Montreal police spokesman Daniel Lacoursiere said. The group had also apparently resisted going in a direction ordered by police.

Montreal police said the overwhelming majority of those arrested were given tickets of more than $600.

Four people will be charged for criminal acts, including assault and attacking police officers.

As the march approached the line of police on Sherbrooke Street, other Montreal officers and Quebec provincial police riot squad members moved in to cut off the other three sides of the street, which at that point intersected St-Denis Street, a trendy avenue dotted with bars, restaurants and theatres.

Police charged the demonstrators snaring them in a pen-like encirclement of grim-faced cops.

Some demonstrators reacted angrily to the tactic while others sat dazed.

The swift police action squeezed the mob together tighter and tighter as the officers advanced and some people begged to be let out, pleading they were bystanders. One photographer was seen to be pushed to the ground and a piece of equipment was heard breaking. Some protesters cursed and yelled at provincial police officers, who ignored the taunts.

Riot officers stood impassively around the corralled demonstrators, feet planted and batons clutched in gloved hands. On a nearby street, a Quebec provincial police officer was seen snapping a rod topped with the flag of the hardcore anti-capitalist Black Bloc and tossing it between two parked cars.

Police on horseback also provided reinforcement as officers sorted out the crowd.

Emmanuel Hessler, an independent filmmaker who had been following the march for a few blocks, said in a telephone interview with The Canadian Press from inside the police encirclement that he was surprised by the action, saying, "Suddenly, there were police all around us."

While the crowd waited to be led away one by one to be handcuffed and sent for processing at a police operational centre -- a procedure expected to take several hours -- a man started reading poetry and the crowd hushed to listen. Someone else sang a folk song. At one point a woman called out the phone number of a lawyer which the mob took up as a chant.

Hessler, 30, was able to tweet to friends, "We are about to get cuffed and off in a bus. Don't know what happens after. Wish me luck."

Some demonstrators who had escaped the police cordon continued to march elsewhere while others milled about beyond the police lines and cheered as buses took the detainees away.

The mass arrests come after five days of escalation of violence and police response during the tuition fee protest which saw tens of thousands of people flood into the streets of Montreal on Tuesday to vent their anger against a special provincial law passed last week to tighten the rules for marches and impose heavy fines on offenders.

While there had been clashes at other points in the dispute, violence marked every night of the long weekend and the first part of the week. Wednesday's demonstration looked as though it was going to break the pattern with an almost party-like atmosphere kicked off in many neighbourhoods by the supportive pot banging that continued in some cases as the demonstration passed by.

In recent days, the percussion-heavy approach has been happening every night at 8 p.m. in Montreal and each night it's gotten bigger and louder and lasted longer. Wednesday night, there were thousands doing it and they spilled out from their houses into the streets in different pockets of the city in crowds that included children, their parents, students and elderly people.

Large numbers joined the student march, which broke off into several splinters during the evening and one woman joked on Twitter that she had broken two wooden spoons and would be bringing a metal one to future pots-and-pans protests.

The percussion-heavy approach is a shift from the bigger, rowdier demonstrations that have been taking place in the downtown every night during the last month.

"It's symbolic because it comes from the revolution in Chile, where there was a dictator in place and there was long tradition of protesting," said Sebastien Barraud, a union representative in the education sector, of the pot banging.

"It also shows that peaceful civil disobedience works. And we're in the process of showing that the polls have no value. A majority of Quebecers are against this government."

Originally from France, Barraud said he also benefited from cheap university fees.

"So I know it's possible. It's just a matter of a political choice."

With files from The Canadian Press