Five workers were killed on Monday in an accident at a sewage treatment plant near Palermo, on the island of Sicily, while another was found unconscious and taken to hospital, firefighters said.
According to Italian broadcaster RAI, the workers suffered from toxic gas poisoning, with one team member managing to get away and raise the alarm. There was no comment from AMAP, the regional group which is responsible for waste water treatment.
The deaths are the latest in a series of workplace fatalities in Italy that have caused anger among trades unions and were highlighted by union leaders in May Day rallies last week.
Rescue services arrived in Casteldaccia, 20 kilometres (12 miles) from Palermo, where seven people were working at the plant. The fire brigade retrieved the bodies of five dead workers and rescued another in serious condition, while one person was found unharmed.
"Full light must be shed on this tragedy," Italy's Prime Minister Giorgia Meloni said on X, expressing her support for the families of the victims and the worker being treated.
The accident occurred just a few weeks after an explosion at a hydroelectric power plant near Bologna, in northern Italy, where seven workers died during maintenance operations.
"We can no longer speak of accidents at work, but of an unacceptable slaughter that calls for a commitment to ensure better safety conditions for workers," Giorgio Mule, deputy president of the Italian lower house of parliament, said on X.