An explosion on Tuesday at a hydroelectric plant in northern Italy killed at least three workers and seriously injured five others, a regional fire chief said.

At least four other people were missing.

The explosion occurred at the hydroelectric plant at the Suviana Dam, some 70 kilometres (40 miles) southwest of Bologna.

The mayor of the nearby town of Camugnano, Marco Masinara, said the explosion happened nine levels below ground during work on turbines, the daily il Resto di Carlino reported. He indicated there were difficulties in reaching the victims.

Video provided by firefighters showed smoke rising from underground at the lakeside powerplant belonging to the Enel power company.

The artificial Suviana Lake was formed by the construction of a dam from 1928-32 and located in a regional park at an altitude of 500 metres (1,640 feet).

Enel Green Power said in a statement that there was no damage to the dam.

Italian premier Giorgia Meloni said she was following the “terrible” news and expressed solidarity with the victims and their families.