Protesters have been spotted hurling flares, smashing store windows and setting fires in eastern Paris on Thursday as thousands in the French capital are marching against President Emmanuel Macron’s plan to reform the pension system.

The chaos comes as a general strike launched alongside the march has created a travel nightmare for tourists and locals, prompting the closure of the Eiffel Tower and dozens of subway stations, while hundreds of flights in and out of the city have been grounded.

Associated Press reporters saw demonstrators destroy a bus shelter as masked activists ran and threw projectiles on the sidelines of an otherwise peaceful march.

Protesters also set fire to a construction trailer and started blazes in the neighborhood around the Gare de l’Est train station where the march began. Other images showed demonstrators clashing with riot police.

Paris deployed 6,000 police for the march and even barricaded the presidential palace — but held back as the violence began. Firefighters now are trying to extinguish the flames.

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Many protesters are wearing yellow vests representing France’s year-old movement for economic justice. Eighteen protesters reportedly were detained before the planned march started, and embassies are warning tourists to stay away from the area.

But many are already finding themselves stuck as much of the city’s regional trains and subways are not operating.

A map posted online by France’s state-owned transportation company showed numerous subway lines completely out of service and dozens of stations closed. Videos and images shared on social media depicted several of the city’s metro stations – often filled with workers and tourists heading to some of the world’s most popular attractions – completely empty.

Signs at Paris’ Orly Airport showed “canceled” notices, as the civil aviation authority announced 20 percent of flights were grounded.

Some travelers showed support for the striking workers, but others complained about being embroiled in someone else’s fight.

"I arrived at the airport this morning and I had no idea about the strike happening, and I was waiting for two hours in the airport for the train to arrive and it didn't arrive,” said vacationer Ian Crossen, from New York. "I feel a little bit frustrated. And I've spent a lot of money. I've spent money I didn't need to, apparently.”

Vladimir Madeira, a Chilean tourist who had traveled to Paris for vacation, said the strike has been “a nightmare.” He hadn’t heard about the protest until he arrived in Paris, and transport disruptions had foiled his plans to travel directly to Zurich on Thursday.

Beneath the closed Eiffel Tower, tourists from Thailand, Canada, and Spain echoed those sentiments.

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Bracing for possible violence and damage along the route of the Paris march, police ordered all businesses, cafes, and restaurants in the area to close. Authorities also issued a ban on protests on the Champs-Elysees avenue, around the presidential palace, parliament and Notre Dame Cathedral.

The subway station closures prompted many commuters to use shared bikes or electric scooters despite near-freezing temperatures. Many workers in the Paris region also worked from home or took a day off to stay with their children, since 78 percent of teachers in the capital were on strike.

Organizers of the march hope for a mass outpouring of anger at Macron for his centerpiece reform, seen as threatening the French way of life. Macron himself remained “calm and determined” to push it through, a top presidential official told the Associated Press.

To Macron, the retirement reform is central to his plan to transform France so it can compete globally in the 21st century. The government is arguing that France’s current pension system – which is divided into 42 different sectors based on occupation – isn’t economical and is in need of an overhaul.

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Macron is hoping to create a unified system where the extent of pension benefits a French worker receives is linked to the number of days they have worked, according to the BBC.

But unions say a universal system would force workers to remain on the job beyond the legal retirement age of 62 — or face a steep drop in the value of their benefits, The Guardian reports.

Elsewhere around France, thousands of red-vested union activists marched through cities from Marseille on the Mediterranean to Lille in the north.

It’s not clear how long the strike will last. Transport Minister Elisabeth Borne said she expects the travel troubles to be just as bad Friday.

Unions say it’s an open-ended movement and hope to keep up the momentum at least for a week, in hopes of forcing the government to make concessions.

Joseph Kakou, who works an overnight security shift in western Paris, walked an hour across the city to get home to the eastern side of town on Thursday morning.

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“It doesn’t please us to walk. It doesn’t please us to have to strike,” Kakou told The Associated Press. “But we are obliged to because we can’t work until 90 years old.”

After extensive meetings with workers, the high commissioner for pensions is expected to detail reform proposals next week, and the prime minister will release the government’s plan days after that.

The Associated Press contributed to this report.