The cause of the blast at the dam on Lake Suviana, located between the cities of Bologna and Florence and managed by energy group Enel, was not immediately clear.

The explosion occurred around 1500 local time (1300 GMT), the spokesperson said.

Marco Masinara, the mayor of the local town of Camugnano, said a fire broke out below ground level, adding that "the plant is all below the level of the lake, at about 30 metres' depth."

He told Italy's Ansa news agency that initial information suggested that work was being done on a turbine at the time of the accident.

"I have been told that the fire brigade are trying to get access but are having difficulties," he added.

(Reporting by Claudia Cristoferi, Writing by Keith WeirEditing by Giulia Segreti)