Chronic overcrowding in some of Europe's beloved tourism hotspots is fuelling an angry backlash, from polite protest to "Go Home" graffiti and even physical intimidation.

Across southern Europe, from the choked boulevards of Gaudi's Barcelona to the swarms of cruise liners disgorging passengers into Croatia's medieval Dubrovnik, residents are complaining that a sharp rise in tourism is making life intolerable.

The backlash has sparked concerns for one of the region's biggest economic drivers and prompted authorities to act.

Rome is considering limiting visitor numbers to parts of the eternal city, such as the Trevi fountain. Dubrovnik plans to limit cruise ships. Barcelona is planning a new tourism tax.

Rome is considering limiting visitor numbers to parts of the eternal city, such as the Trevi fountain

In Venice last month, residents marched through a throng of visitor to protest against uncontrolled tourism. They did so behind a banner: "My future is Venice".

Youth activists plan a similar protest in San Sebastián, northern Spain, later this month.

In Barcelona, where anger has been brewing for some time, some graffiti has turned menacing. One slogan, featuring a black silhouette with a red target on its head, reads: "Why call it tourist season if we can't shoot them?"

Spanish Prime Minister Mariano Rajoy intervened this week after some anti-tourist anger turned physical. A video emerged of masked activists setting off flares outside a restaurant full of tourists on the island of Palma de Majorca. They then entered the restaurant and threw confetti at frightened diners.

Rajoy described the activists as "extremists going against common sense". Tourism makes up 12% of Spain's economy.

Similar videos were released this week under the slogan "tourism kills neighbourhoods". In one, several hooded individuals stop a tourist bus in Barcelona, slashing the tyres and spray-painting the windscreen.

"We haven't seen any of that yet but we heard that the locals are not that fond of tourists," said 20-year-old Dutch tourist Roel Theuniszen as he took a break from cycling on a rental bike outside Barcelona's popular Ciutdella Park.

"It's important to try not to stand out as a tourist in a city like Barcelona to have a good experience ... Also, it's important to be more considerate (as a tourist)."

Tourism to southern Europe has surged over the past two years, partly because visitors are choosing the region over other Mediterranean destinations where security fears are a concern, such as Tunisia, Egypt and Turkey.

Foreign visitors to the glories of Rome, Florence and Venice surged 31.5% between 2009 and 2015

Visitors to Spain jumped 12% in the first half of 2017 to 36.4 million. Barcelona draws at least 11 million visitors a year and is planning a new tax that will hit cruise ships: 65 euro cents for each visitor staying less than 12 hours. About 750 cruise ships docked at Barcelona last year.

Tourist arrivals in Italy rose a modest 1% in 2016 to almost 56 million, but hotel stays were up 4.8% in the first half of 2017. Foreign visitors to the glories of Rome, Florence and Venice surged 31.5% between 2009 and 2015.

Resident anger has prompted Italian authorities to monitor tourists more closely, with special patrols in Rome's historic centre and fines for people who paddle in the fountains.

Venetian authorities experimented with limiting access to certain areas during a festival for the first time in the city's history in July, shortly after the street protest.

Some officials have proposed ticket-only access to St Mark's Square, which heaves with people in summer, but local and national authorities are against this.

"The city has completely lost its identity," said Alessandro Bressanello, a Venetian actor who joined the 25 April civil group which wants limits imposed on new tourist accommodation and better management of tourist flows.

"Everyone should be able to come here but this invasion creates real problems for Venetians and the city, it creates infinite amounts of rubbish and noise," Bressanello said.

More than 5,000 tourists from cruise liners flocked to Dubrovnik in a single day in June on top of thousands vacationing in the city

Authorities in the town of Dubrovnik, on Croatia's Adriatic coast, are considering cutting the limit on daily visits by cruise liners to two from up to five currently, due to concerns of overcrowding at the Unesco World Heritage site.

More than 5,000 tourists from cruise liners flocked to the walled town in a single day in June on top of thousands vacationing in the city. Unesco has even warned that Dubrovnik's World Heritage status is at risk.

A walk through the old town's 300-meter-long (330-yard-long) pedestrian zone can take 40 minutes in peak season. The old town's resident population is dwindling as residents move away to escape the crowds, traffic jams and noise.

"It must never happen again that more than two cruise ships come to the town at the same moment," Dubrovnik Mayor Mato Frankovic said recently.

Croatia overall saw a 10.5% jump in tourists last month from a year earlier, tourism association data shows.

For its part, Cruise Lines International Association says it expects more tourism restrictions in some places and that it is committed to sustainable tourism.

Elsewhere, Portugal expects a record 27 million visitors this year and Greece a record 28 million, but neither has seen a big backlash. In France, too, relations between tourists and residents appear good.