The closure of sections of Italy's main steel plant as part of an investigation into health and environmental pollution sparked heated reactions on Friday, as hundreds of workers went on strike.

"In this serious moment for the country's economy, taking actions this traumatic against the biggest steelworks factory in Europe is an unbearable blow," said the head of Italy's manufacturing association Pier Luigi Ceccardi.

Some 5,000 people work in the most polluting sections of the ILVA plant, which were closed Thursday while magistrates investigate whether their fumes endanger the health of employees and residents in the southern city of Taranto.

ILVA is owned by the Riva Group, one of Europe's largest steel producers.

Hundreds of workers fearing for their jobs blocked main roads bringing the town to a stand-still and demanding protection from the government, while trade unions called on Italy's President Giorgio Napolitano to intervene.

Eight ILVA executives were 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 August 3.

"The Italian steel industry will react strongly to any attempt to call into question, for some sort of distorted environmentalist ideology, the industry's presence on Italian territory," steel producers' association Federacciai said.

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.

ILVA employs around 11,500 workers in the Puglia region, and employees and industrial figures have slammed the closure.

"It's right that Taranto should be cleaned up, but ILVA needs to stay open. There is no future without this factory," one striker told the ANSA news agency.

Environmental association "Taranto Breathes" hailed the magistrates' decision to shut down areas of the plant as "a historic turn-around," 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 insisted Thursday he would call on the magistrates to review the case and said the town's output should be sustained.