People attend a demonstration in Paris, Dec 5, 2019. (THIBAULT CAMUS / AP)

PARIS — Paris police fired tear gas at demonstrators Thursday as the Eiffel Tower shut down, France’s high-speed trains came to a standstill and hundreds of thousands marched nationwide in a strike over the government’s plan to overhaul the retirement system.

At least 90 people were arrested in Paris by evening as the protests wound down.

Police said 65,000 people took to the streets of the French capital, and over 800,000 nationwide in often-tense demonstrations aimed at forcing President Emmanuel Macron to abandon pension reform.

The Eiffel Tower shut down and France's high-speed trains came to a standstill as over 800,000 took to the streets nationwide

The open-ended walkout by the country’s unions represents the biggest challenge to Macron since the yellow vest movement against economic inequality erupted a year ago.

READ MORE: Mass strike over pensions tangles transport across France

Opponents fear the changes to how and when workers can retire will threaten the hard-fought French way of life. Macron himself remained “calm and determined” to push it through, according to a top presidential official.

In Paris, small groups of masked activists smashed store windows, set fires and hurled flares on the sidelines of a march that was otherwise peaceful. Demonstrators also shot firecrackers at police in body armor. Some journalists were mugged in the street.

The Louvre closed some of its galleries, and the Palace of Versailles shut down. Subway stations across Paris closed their gates, high-speed TGV trains canceled their runs, and nearly 20 percent of flights at Paris’ Orly Airport were reported grounded.

Many visitors, including the US energy secretary, canceled plans to travel to one of the world’s most popular tourist destinations.

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

"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.”

The closed Eiffel Tower is seen in Paris, Thursday, Dec 5, 2019. (LUDOVIC MARIN / AFP)

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

Paris authorities barricaded the presidential palace and deployed 6,000 police officers. Police ordered all businesses, cafes and restaurants in the area to close and detained 71 people before the demonstration even started.

Authorities banned protests in the more sensitive neighborhoods around the Champs-Elysees avenue, the presidential palace, Parliament and Notre Dame Cathedral.

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Health workers showed up to decry conditions in hospitals. Students pointed to recent student suicides and demanded government action. Environmentalists emphasized that climate justice and social justice are one and the same.

And young and old roundly condemned the new retirement plan, which they fear would take money out of their pockets and reduce the leisure period the French expect have come to expect in the last decades of their lives.

Skirmishes broke out between police firing tear gas and protesters throwing flares in the western city of Nantes, and thousands of red-vested union activists marched through cities from Marseille on the Mediterranean to Lille in the north.

The empty Lille Flandres train station is pictured in Lille, northern France, Dec 5, 2019. France's vaunted high-speed trains came to a standstill as unions launched nationwide strikes and protests over the government's plan to overhaul the retirement system. (MICHEL SPINGLER / AP)

Lacking public transportation, commuters used shared bikes or electric scooters despite near-freezing temperatures. Many people in the Paris region worked from home or took a day off to stay with their children, since 78 percent of teachers in the capital went on strike.

The big question is how long the walkout will last. Transport Minister Elisabeth Borne said she expects the travel troubles to be just as bad on Friday, and unions said they will maintain the Paris subway strike at least through Monday.

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

“It doesn’t please us to walk. It doesn’t please us to have to strike,” he said. “But we are obliged to, because we can’t work until 90 years old.”

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The deeply unpopular Macron is expected to reveal the details of his plan next week. The government has promised not to touch the official retirement age — 62, though lower for certain physically demanding occupations — but the plan will encourage some people to work longer.

To Macron, the retirement reform is central to his plan to transform France so it can compete globally in the 21st century. The government argues France’s 42 retirement systems need streamlining.