Three corpses were found on Tuesday shortly after the fire and explosion rocked the plant owned by Enel Green Power, part of Enel Group, on the shores of the artificial Lake Suviana. Two other workers remain unaccounted for.

Divers recovered the two bodies from the ruins of a turbine hall some nine levels -- 40 metres or so -- below the lake.

One of them was named as Adriano Scandellari, who was 57 and worked for Enel Green Power.

The cause of the accident has not been established and Italian prosecutors have launched an investigation, as is mandatory in such cases.

The deaths have compounded already widespread concerns expressed by trade unions about workplace safety in Italy, after a series of fatal accidents in factories and building sites.

Enel staff went on strike for eight hours over the issue on Thursday, while workers in other sectors held a previously announced four-hour stoppage and demonstrated in towns and cities across Italy.

Protesters held banners saying "Adesso basta!" ("Enough now!") to make their point that it was time to stop fatal accidents in workplaces.

Unions said that over half of Enel workers had joined the strike but the company put the figure much lower, at under 9%.

(Reporting by Claudia Cristoferi, Giancarlo Navach and Francesca Landini; Writing by Keith Weir; Editing by Gavin Jones and David Evans)