Thousands of Italians took to the streets in the southern city of Taranto Thursday in rival protests over the closure of one of Europe's largest steel plants due to pollution concerns.

The impoverished industrial port has become the scene of a fierce stand-off between those who want the deadly ILVA plant closed and the thousands of families that depend on it at a time of worsening economic crisis in Italy.

A trade union-organised demonstration against the closure was disrupted by groups of environmentalists, who had to be restrained by police in riot gear.

"It's unthinkable to lose 20,000 jobs. This demonstration calls attention to a national emergency," CISL union head Raffaele Bonanni told the crowds in Taranto's main square, as the rival protesters threw eggs and smoke bombs.

ILVA, which is owned by the Riva Group, employs around 11,500 workers, including some 5,000 in the most polluting sections of the plant.

Sections of the plant were closed last week while magistrates investigate whether their fumes endanger the health of employees and residents.

Eight ILVA executives have been put under house arrest following expert findings that chemicals spilling from the plant are behind high cancer rates.

They are set to appear before Taranto magistrates on Friday, when the decision to shut down the factory will be appealed.

"The ILVA problem raises the issue of industrial equipment in our country. If we do not find solutions, we will be forced to import steel from abroad," the head of the CGIL union, Susanna Camusso, said.

"We want investments to be made with working plants and ask the government to guarantee the company's operations," she added.

An Italian study last year found that Taranto suffered from a "mortality excess" of between 10 and 15 percent, due to the release of dioxin and other chemicals causing cancer, respiratory and cardiovascular diseases.

Environmental association "Taranto Breathes" hailed the magistrates' decision last week to shut down areas of the plant as "a historic turnaround," and praised the courts "for intervening where politics has failed."

The government has promised a 336-million-euro ($414-million) clean-up programme for the city. Environment Minister Corrado Clini has called on magistrates to review the case and said the plant should be kept open.