Orchestra provides a selection of protest songs for French demonstrations

They are an unexpected sight: a 400-piece orchestra playing classical music in central Paris as thousands of protesters wave placards and clash with police.

The musicians are part of the all-volunteer Orchestre du Nouveau Monde, founded four years ago as a way of using music to raise awareness of social issues, and they’ve become a fixture at many recent protests in Paris.

On Saturday, the orchestra was accompanied by 100 singers at the Place de la République. They’d planned to play a selection of classic protest songs − including Bella Ciao, The Internationale and El pueblo unido jamás será vencido − as well as La Marseillaise, the French national anthem, and soundtracks from the Hunger Games and the Avengers films.

The musicians barely got through their warm-up when they were overcome by tear gas that filled the square as police battled protesters.

“We tried to resist and to play through the gas, but it was too hard,” recalled Constant Sala, 24, who plays percussion and arranges some of the pieces. “A few musicians were really scared. It’s the first time the orchestra has been tear gassed.”

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In a video posted later on Instagram, orchestra conductor and co-founder Étienne Jarrier called the experience “surreal.”

“There was no one left on the square. We were just standing there with our instruments, playing, and they kept firing tear gas,” he said.

The orchestra’s website says the group was launched out of a “desire to create an orchestra of resistance in the face of the world’s challenges, committed to social and climate justice.”

Its mission is to “use music not as a sacred object of beauty but as a tool for activism rooted in current events. Through civil disobedience, we draw attention to current emergencies with strong, peaceful, and sometimes unconventional actions.”

At first the orchestra consisted of some 200 professional and amateur musicians. But its numbers have swelled since it began appearing at the student protests that started across the country about a month ago.

Mr. Sala said he joined to help “politicize classical music and bring it to the heart of the social struggles.” He recently graduated from university and works part-time in schools helping music teachers while trying his hand at composing.

“I was a student a few weeks ago and I know how hard it is − and how hard it is to feel like we’re not listened to,” he said. “The social struggle is real, and we are here to put the light on the high-schoolers.”

The orchestra has become well-known for its stunts.

They’ve made appearances outside the headquarters of the far-right National Rally party and played Maréchal, les voilà!, a popular song sung by the French Resistance during the Second World War that mocked France’s authoritarian Vichy government.

Earlier this month, the orchestra performed in front of the Paris City Hall during a student protest. Mr. Jarrier came dressed as Darth Vader and led the musicians in a rendition of the theme from Star Wars.

More than 500,000 people attended protests in Paris and several other cities last Saturday. While most of the demonstrations were peaceful, some deteriorated into the worst violence France has seen in years. More than 2,000 people were arrested, some 3,000 shops and restaurants were looted, and more than 600 police officers and firefighters were injured.

Authorities have responded this week with curfews in some cities and bans on demonstrations in certain neighbourhoods. Police are bracing for more potential violence Saturday when another major round of protests is expected to take place.

In his video, Mr. Jarrier said the group wasn’t deterred by the violence last week and vowed to press ahead with more performances. “Let’s stick together,” he said. “We’ll see each other again soon for more revolutionary adventures.”

Mr. Sala said he, too, was not put off by the violence and felt it was almost inevitable. “Even if we are peaceful, sometimes the government doesn’t listen,” he said in an interview. As for the looting: “With the orchestra, we don’t think it’s the best way to show support or to demand things. But the struggle is real.”

He’s not sure when the orchestra will play again, given the various bans and curfews. “We want to, we absolutely want to,” he said. “We want to rest for a bit and then come back stronger.”