Venice (AFP) - A massive cruise ship lost control in Venice Sunday, crashing into a wharf and sparking a fresh controversy over the damage the mammoth vessels cause to one of the world's most famous cities.
Footage posted to social media showed people on the harbour fleeing as the 13-deck MSC Opera, which suffered an engine failure, scraped along the dockside before knocking into a luxury tourist boat.
"When we saw the ship bearing down on us, everyone began shouting and running," a sailor who was on the River Countess tourist boat was quoted as saying by Italian media.
"I didn't know what to do. I got away quickly, jumping to get on shore," said the man, who was not named.
Four tourists were slightly injured in the accident at San Basilio-Zattere in Venice's Giudecca Canal, port authorities said.
The foreigners, aged between 67 and 72 years old, were from Australia, New Zealand and the United States, according to media reports.
The incident came just days after a river cruise ship collided with a sightseeing vessel in Budapest, killing seven people and leaving 21 missing.
The Opera -- which can carry more than 2,500 passengers and boasts a theatre, ballroom and water park for children -- has suffered mechanical trouble before in 2011, during a Baltic cruise.
- Ship unable to stop -
"The MSC ship had an engine failure, which was immediately reported by the captain," Davide Calderan, head of a tugboat company involved in accompanying the ship into its berth, told Italian media.
"The engine was blocked, but with its thrust on, because the speed was increasing," he said.
The two tug boats that had been guiding the ship into the Giudecca tried to slow it, but one of the chains linking them to the giant snapped under the pressure, he added.
"I could see the prow coming closer, and I thought it would hit my house. The noise was deafening," one Venetian resident was quoted as saying by Italian media.
The accident has reignited a heated row in Venice over the damage caused to the city and its fragile ecosystem by cruise ships that sail exceptionally close to the shore.
While gondoliers in striped T-shirts and woven straw hats row tourists around the narrow canals, the smoking chimneys of mammoth ships loom into sight behind the city's picturesque bell towers and bridges.
Critics say the waves the ships create are eroding the foundations of the lagoon city, which regularly floods, leaving iconic sites such as Saint Mark's Square underwater.
"What happened in the port of Venice is confirmation of what we have been saying for some time," Italy's Environment Minister Sergio Costa wrote on Twitter.
"Cruise ships must not sail down the Giudecca. We have been working on moving them for months now... and are nearing a solution," he said.
- 'Risk of carnage' -
WWF Italy described the incident as "an important alarm bell to which it would be madness not to listen".
Italy's Transport Minister Danilo Toninelli said the government would come up with a "definitive solution" by the end of June.
It is not the first time the government has made such promises. In 2013 it banned ships weighing more than 96,000 tonnes from the Giudecca Canal.
The ban was in part a response to the deadly 2012 Costa Concordia disaster, in which the 115,000-ton cruise ship crashed into Giglio island off Tuscany after its captain sailed too close to the shore.
But the law was later overturned by a regional court, which ruled that safety or environmental risks had not been proven.
Two years ago the government announced that larger ships would be diverted away from the historic centre -- but failed to follow through on the pledge.
MSC Cruises, founded in Italy in 1960, is a global line registered in Switzerland and based in Geneva.
One of its cruise ships, the MSC Preziosa, collided with a passenger embarkation ramp as it entered port in Venice in 2014, according to the local La Nuova daily.
The Opera, built 15 years ago, suffered a power failure in 2011 in the Baltic, forcing some 2,000 people to be disembarked in Stockholm rather than continuing their Southampton to Saint Petersburg voyage.