MILAN (Reuters) - Police fired tear gas at demonstrators on Friday as violent protests marred the start of the Milan Expo, a global fair the government had hoped would help to put a new face on Italy after years of economic decline.
Thick clouds of smoke from burning cars filled parts of central Milan, where groups of protesters, their faces masked against the fumes, threw stones and petrol bombs and faced off against lines of police in riot gear.
The confrontation broke out after an opening ceremony at the Expo site where Prime Minister Matteo Renzi hailed the start of a six-month-long showpiece of culture and technology that focused on the theme of sustainable food production.
The fair mobilised a range of left-wing protesters, from anti-globalisation and environmentalist activists to students and anti-austerity campaigners, who see it as a symbol of waste and corruption. Thousands of police had been deployed to counter the threat of violence.
Renzi has been counting on the event to reinforce signs of recovery after years of recession that have hit young people especially hard.
"All you experts who kept saying 'We'll never do it' -- this is your answer," he said at the opening. "I like to think that tomorrow begins today."
Instead, the elegant centre of Milan was transformed into a battle ground, with sirens and bangs from flash bombs and firecrackers ringing out against the shouts of protesters. Eleven police suffered minor injuries.
The main part of the demonstration was halted by police vans blockading the street, but breakaway groups of masked demonstrators fought running battles in the rain that left streets littered with makeshift barricades and debris.
Police detained a number of demonstrators but there was no immediate official estimate of the damage, which included smashed windows and street fittings and burned-out cars.
As the violence petered out in the evening, police blocked off the area around La Scala opera house, where a performance of Puccini's "Turandot" rounded off the opening day ceremonies.
Renzi declined to comment as he entered La Scala in evening dress for the opera.
Some 10 million tickets are already sold for the expo and officials are counting on some 20 million people attending. They hope overall revenues will top 10 billion euros ($10.75 billion), half from foreign visitors drawn to Milan.
Matteo Salvini, leader of the anti-immigrant Northern League party and Renzi's main political rival, said Interior Minister Angelino Alfano, whose department is responsible for civil order, should resign.
"Renzi and Alfano, are you going to pay for the damage citizens have suffered?" he said in a statement.
The event had already been hit by a corruption investigation that saw several officials arrested and by cost overruns and construction hold-ups. Large parts of the site were not ready for opening day.
Pope Francis, who spoke via a televised link-up to the opening ceremony, referred to the irony of a global spectacle dependent on corporate sponsorship deals being devoted to sustainable development and feeding the poor.
"In certain ways, the Expo itself is part of this paradox of abundance, it obeys the culture of waste and does not contribute to a model of equitable and sustainable development," he said.
The real protagonists of the event should be "the faces of the men and women who are hungry, who fall ill and even die because of an insufficient or harmful diet," he said.
Cultural events, futuristic architecture, a "supermarket of the future" and dozens of restaurants fill the site, which required more than 1 million square metres (250 acres) of farmland on the outskirts of Milan to be concreted over.
In all, more than 140 countries are taking part. China, an increasing presence in Italy after a string of high-profile business acquisitions, is particularly well represented.
Writing by James Mackenzie, Additional reporting by Danilo Masoni, Editing by Angus MacSwan