An explosion at a hydroelectric power plant in northern Italy has killed four people and left several missing.
The explosion occurred underwater at a factory on the shores of Lake Sviana, 70 kilometers from the city of Bologna.
The affected area is located 30 meters (100 feet) below the lake's surface.
The mayor of the nearby town of Camugnano told Ansa news agency that the fire appeared to have started during maintenance work.
Marco Masinara said rescue teams were struggling to gain access and the accident was “serious”.
Three of the four people who died in the disaster were between 35 and 73 years old.
Bologna Governor Attilio Visconti said a turbine exploded on the eighth floor, causing a fire and flooding the floors below.
One of the divers involved in the search and rescue operation told Italian newspaper La Repubblica that they managed to reach the seventh floor underground, but were unable to reach the three people trapped further down.
Several people are known to have suffered severe burns from the explosion, which occurred at around 15:00 (13:00 Japan time). They were taken by helicopter to a nearby hospital.
According to Italian media, two men were taken to intensive care.
Bologna Mayor Matteo Lepore, who visited the site on Tuesday night, said the situation for search teams dozens of meters underground was “very complicated”. He said this was one of the worst labor tragedies in Italy's recent history.
The city's chief prosecutor, Giuseppe Amato, told Italian media that the factory was safe and an investigation would begin as soon as the missing people were found.
“We will not stop until we find it,” Luca Cali said on behalf of the firefighters.
The cause of the accident has not yet been determined, but the incident could heighten concerns expressed by trade unions about workplace safety in Italy.
Two of the country's largest labor unions had already planned to hold a four-hour strike across the country on Thursday to protest the issue.
Area fire chief Francesco Notaro said firefighters and police were “all working to ensure the safety of the facility.”
Lake Sviana is an artificial lake located in the Appennines near Bologna. This lake was formed after his 1932 dam construction.
Italian Prime Minister Giorgia Meloni thanked rescuers on X (formerly Twitter) and said she was watching news of the explosion with “concern.”
The power plant is owned by Italian energy giant Enel Green Power.
The company said there was no evidence of damage to the dam, but the power plant had ceased production.