ROME — The Italian army moved into Naples yesterday as tensions over the city’s mounting trash crisis erupted in violence.

Entire districts of the city are lying submerged under more than 5,000 tons of waste. The pile is growing at the rate of 800 tons a day.

No garbage has been collected in Naples since December 21, when the city’s dumps reached their capacity.

While the residents are furious at the stink, and the risk of disease, there have also been protests at plans to create new dumps or reopen old ones.

Riots broke out yesterday at Pianura, the site of an enormous open-air dump that the locals say pollutes the area with deadly dioxins.

Four buses were set alight during the night and police were struck with a hail of stones as they tried to dismantle temporary roadblocks.

More than a thousand protesters laid metal railings, chunks of concrete and old tires across the road to prevent workers and trucks from entering the dump. One group used a bulldozer to wreck the surface of the road and to bring down trees in front of the gate.

Anti-riot officers charged the crowd with batons, and at least three people were taken to the hospital. One unnamed teenager was injured after his scooter skidded on a pile of rubbish. However, officials temporarily conceded defeat in reopening the dump.

Other protesters blocked the main A1 motorway at Caserta, the spine of Italy’s road network that connects Naples to Rome, Florence, and Milan. In response, Prime Minister Prodi sent in the army to restore calm and to start shifting the trash from the city.

“We are taking charge,” he said, “because the world is watching, and I do not want them to have this negative image of Italy.”

Army engineers used bulldozers to clear waste from schools in the Caserta region. The government called for the schools to be opened, but no students arrived. Clemente Mastella, the justice minister, said the dead hand of the Camorra, or Neapolitan mafia, was behind the crisis.

“People who set fire to buses are not citizens, but usually people sent by the Mafia,” he said.

It is in the Camorra’s interests for rubbish to build up in the city, since the clans own most of the rubbish recycling companies that would eventually win contracts to dispose of the waste.

In the past, corrupt firms have been found to be shipping waste to China, where it is buried, instead of recycling it.

Mafia families also profit from buying properties in the troubled areas, where prices have become depressed by the continuing rubbish crisis. In addition, the Camorra is said by the police to bring lorry-loads of waste to Naples from factories in northern Italy for fees that undercut legal competitors, adding to the trash piles.

Sandro De Franciscis, the head of the council of Caserta, said: “We are on our knees, we are desperate and we do not have the power to do anything about it.”