An explosion at an Italian hydroelectric power plant on Tuesday killed at least four people and left five missing, an official said.

Three people were also injured in the incident at the Bargi plant run by Enel Green Power located on Lake Suviana, the official from the Bologna prefecture in central Italy told AFP.

Fire service images showed smoke rising from the plant on the water's edge where firefighters searched for the missing following the early afternoon blast.

The mayor of the nearby town of Camugnano, Marco Masinara, called the explosion a "terrible workplace accident" that affected the "entire community".

"It seems there was a floor slab collapse and rescue is difficult as a lot of water entered inside the eighth basement floor," he said.

No official cause has yet been determined.

Bologna fire department head, Calogero Turturici, told local television that at least one person was seriously injured.

Prime Minister Giorgia Meloni said on social media that she was "following with apprehension the terrible news regarding the explosion."

Enel Green Power, the renewables unit of energy giant Enel that operates the plant, said it was coordinating with authorities.

In a statement to AFP, it said "a fire affected one of the two groups of the Bargi plant" in the province of Bologna.

"Following investigations, the dam basin of the Bargi plant was not damaged and is safe," it said.

Production was halted, but there was no impact on local or national supply, it said.

"The company informs that it is continuing to operate in line with all the necessary safety measures as per internal procedures to guarantee the evacuation of its staff."