An explosion at an Italian power station on Tuesday killed at least three people and left 4 others missing. Another four people were hospitalized with serious burns.

The incident occurred at around 3 p.m. local time at a hydroelectric power station on Lake Suviana in the Apennine Mountains, some 70 km south of Bologna. All those involved were working at the plant when the explosion took place.

The bodies of the three victims were recovered in the afternoon, Bologna prefect Attilio Visconti told state-run Rai News 24 channel.

As of Tuesday night, a search and rescue operation is underway to locate the four persons still unaccounted for, who had been on the ninth floor underground of the plant, the official said.

The Fire Dept. reported that some 60 firefighters, including scuba drivers, were involved in the effort. The Civic Protection was also put on alert and would be ready to support, according to regional authorities.

According to initial reports, a fire broke out on the eighth floor underground some 30 meters deep in one of the two units of the plant, and the explosion followed shortly after.

The dam reservoir at the plant was not damaged by the explosion and was safe, according to Enel Green Power, a company that manages the station. The company added that production at Suviana was halted, but the electricity supply at the local or national level was not impacted.

Both President Sergio Mattarella and Prime Minister Giorgia Meloni sent their condolences to those involved. A ceremony to commemorate the victims will be held at parliament on Wednesday.