Welcome to Venice. That’ll Be 5 Euros, Please.

Pulling into the Santa Lucia train station in Venice on Thursday morning, passengers were told via an overhead announcement that they might have to pay a five-euro fee to access the city’s historic center. Failure to pay could result in a fine from “50 to 300 euro,” the announcement said.

Outside the station, police officers in riot gear lingered, while a flock of assistants in colorful safety vests stopped arriving travelers to ensure that they had a QR code indicating that they had registered to visit on a city website. Those who hadn’t were directed to a booth where they could. After registering, overnight visitors were sent on their way without paying, but people planning to stay just for the day were charged (though there were other exemptions).

It was a new welcome to Venice, the first city in the world to charge day visitors a nominal entrance fee, a measure city officials hope will help counter overtourism.

“I only found out because my partner texted me this morning to say it was happening,” said Lorraine Colcher, a hospital administrator from Wirral, England, in line at the booth. “I thought he was joking.”

And she didn’t think that people should have to pay for the privilege of seeing a “beautiful city that everyone wants to visit,” she said.

Not far from the station, hundreds of protesters were making a lot of noise. For them, charging an entrance fee was a worrisome step in bringing Venice closer to what many fear the city will become if tides don’t turn: a theme park. Blowing whistles, they handed out fake tickets reading, “Welcome to Veniceland.” Some held signs saying, “Venice is not for sale” and “Stick It To The Ticket,” and chanted, “We want to take back our city.”

“A ticket doesn’t resolve overtourism,” said Renata Marzari, a retired teacher from Venice who was among the protesters.

Like other locals, she acknowledged that an influx of tourists — which last year reached nearly 20 million — could be a challenge. Often, she said, it involved physical collisions, including “pointing accidents, when you walk into a suddenly raised hand, or photo accidents, when they back into you as they’re looking into their phones.” But the ticket, which applies only to day visitors arriving between 8:30 a.m. to 4 p.m., was “ridiculous,” she said. She added, “They could make more money charging for every cigarette butt that gets tossed on the ground.”

Venice is only one of dozens of cities, including Amsterdam, Athens and Barcelona, grappling with a glut of tourists. Speaking in front of the train station Thursday morning, the city’s mayor, Luigi Brugnaro, said he’d been contacted by other places interested in the initiative, but he wouldn’t say which ones, “for reasons of confidentiality.”

Floating on water crisscrossed with canals, Venice, which tradition says was founded in 421, though that date is debated, is exceptionally fragile. Last year experts at UNESCO, the United Nations’ culture agency, recommended it be put on the list of its endangered World Heritage Sites, listing mass tourism as a main concern. Venice stayed off the “in danger” list after the access fee was approved, but UNESCO officials said in a statement that “further progress still needs to be made.”

Critics of the fee say that it will do little to combat the city’s real problems, which have pushed many to leave. The resident population in the city center has eroded to fewer than 49,000 people, from nearly 175,000 in 1951, according to municipal statistics. They list a lack of affordable housing, because of short-term rentals; a decline in services like schools and transportation; and the encroachment of the tourist industry into practically all walks of life.

Federica Toninelli, a member of a local association that advocates affordable housing in Venice, saw the ticket as “propaganda” and said the city must put “the needs of residents at the center of policies.” City officials need to “take strong steps that would bring the city back to a level of more manageable tourism,” she said.

Otherwise, “this is how a city dies,” said Nicola Camatti, an economics professor and expert in tourism at Ca’ Foscari University of Venice.

Franca Caltarossa, who once ran a municipal after-school program that she said lost much of its funding under the current mayor, said that “tourism has distorted the city.”

“Venice is a living city, not a theme park,” she said.

A 2020 study by tourism experts at Ca’ Foscari, Venice’s main university, suggested that the optimum number of visitors to Venice per day was around 52,000 people, about a quarter of them daily excursionists. But Venice is not capping the number of visitors.

“We are contrary to limiting the number of visitors; this is an open city,” said Michele Zuin, the city councilor in charge of the budget. Instead, the city hoped that day visitors — around 10 million last year — would plan to come on off-peak days when the city “is calmer,” Mr. Zuin said.

“We’re convinced that it is a solution to manage day visitors,” he said.

On Thursday, a national holiday in Italy, 113,000 people had registered to enter Venice. Of these, 15,700 paid the access fee, 40,000 were exempt overnight guests, while the remaining visitors — also exempt — included students, workers and relatives or friends of residents.

For 2024, the fee will be applied on 29 peak days as “an experiment,” Mr. Zuin said. Data collected during this phase will assist city officials to better manage resources, and better control the phenomenon, they say. Mr. Zuin said that next year, more days would be added to the fee calender, and fees could be as high as 10 euros.

“Doubling the price is making the city a commodity, nothing more than a theme park, a museum,” said Giovanni Andrea Martini, a local opposition lawmaker. He questioned the usefulness of the fee given that City Hall’s future projects included plans to enlarge the airport and dig new canals in the lagoon so that boats, and even cruise ships, which were banned in 2019, could dock closer. “This means the city will be further suffocated,” he said Thursday, cutting the interview short because a brief scuffle had broken out between the protesters and the police.

At the train station, tourists lined up patiently at the access fee booth to sort out their passes.

Charlotte Dean, a wine merchant, and Caroline Meatyard, a retired schoolteacher, both from England, cheerfully paid the fee. It’s “fair enough,” Ms. Dean said. “Venice is a lovely place, it should be treasured.”