Under a trial scheme, visitors exploring Venice for the day have to buy a five-euro ($5.30) ticket, with inspectors carrying out spot checks at key entry points.
Considered one of the most beautiful cities on the planet, Venice is a top tourist destination -- but is drowning under the weight of the crowds.
Around 13,000 tickets had been sold by late morning, the mayor's office said, either purchased online or at the new ticket office at the Santa Lucia train station.
The "Venice Access Fee" is initially being introduced on 29 busy days throughout 2024, mostly weekends from May to July.
There is no limit to the number of tickets available. Instead, the goal is to try to persuade day-trippers to visit during quieter times.
"I think it's good, because it will perhaps slow down the numbers of tourists in Venice," said Sylvain Pelerin, a French tourist who has been visiting for more than 50 years.
Overnight visitors, who already pay a tourist tax, minors under the age of 14 and others are exempt.
But some residents are strongly opposed to a measure they say curbs fundamental rights to freedom of movement.
Around 300 people protested near the station on Thursday morning, holding up signs such as "Stick it to the ticket!" and "Venice is not for sale!"
"This is not a museum, it's not a protected ecological area, you shouldn't have to pay -- it's a city," Marina Dodino, from the local residents association ARCI, told AFP.
'Soft controls'
Luigi Brugnaro, the mayor of Venice, has said the new scheme is "an experiment," monitored with "very soft controls" and "without queues."
There are no turnstiles or barriers, with inspectors instead carrying out checks at key entry points into the city.
They will be able to fine those without tickets, ranging from 50 to 300 euros.
But an official told AFP none are expected on Thursday as authorities seek to persuade rather than punish.
The scheme is being closely watched as destinations around the world grapple with huge numbers of tourists, who boost the local economy but risk overwhelming local communities and fragile sites.
Venice, spread over more than 100 small islands and islets in northeastern Italy, was listed by UNESCO as a World Heritage site in 1987.
But the numbers of people seeking to experience what the UN cultural body calls an "extraordinary architectural masterpiece" have become overwhelming.
At peak times, 100,000 visitors stay overnight in the historic center of Venice, double the resident population of just 50,000.
Tens of thousands more pour into the city's narrow streets for the day, often from cruise ships, to see sights including St Mark's Square and the Rialto Bridge.
UNESCO threatened last year to put Venice on its list of heritage in danger, citing mass tourism as well as rising water levels in its lagoon attributed to climate change.
Venice escaped the ignominy only after local authorities agreed the new ticketing system.
'New balance'
Authorities had already imposed a ban in 2021 on the massive cruise ships from which thousands of day-trippers emerge daily, rerouting them to a more distant industrial port.
The ticket idea had long been debated but repeatedly postponed over concerns it would seriously dent tourist revenue and compromise freedom of movement.
"The aim is to find a new balance between tourism and the city of its residents," Simone Venturini, the local councilor responsible for tourism, told AFP.
He hopes the initiative will persuade Italians living in the region to avoid busy days such as Thursday, a public holiday in Italy, marking the liberation from the Nazis and Fascism.
But Ashish Thakkar, an American tourist visiting Venice with his wife, questioned how much of an effect the day pass would have.
"If I'm coming all the way from out of the country, five euros just to get access to the city -- I wouldn't mind paying it," he told AFP.
Some residents complain the measures fail to address another major issue -- the expansion of short-term lets through websites such as Airbnb, which are squeezing out long-term tenants.
In Florence, which also suffers from mass tourism, authorities have banned new short-term private holiday lets in the historic center and offered tax breaks for landlords who switch back to ordinary leases.
"You have to start with the houses if you really want to solve the problem of tourism in Venice," said Federica Toninello, a local campaigner.