(Bloomberg) -- An explosion Tuesday at a northern Italian hydro-power plant owned by Enel SpA’s renewable arm left at least three people dead.

Enel, Italy’s largest power supplier, said a fire had impacted a transformer at an Enel Green Power plant in Bargi, in the province of Bologna, without providing further details. 

The incident occurred around 40 meters (131 feet) underground during maintenance to upgrade the facility, and the subsequent explosion led to the collapse of a building’s structure, with a water pipeline breaking and flooding the site, according to Italian news agencies and dailies.

Three deaths have been confirmed as of late Tuesday, a person familiar with the incident said, and five workers were seriously injured, local media reported. Rescue workers continued to search for as many as four missing people, according to the national fire department.

The site was shut immediately after the accident, but the plant’s dam wasn’t affected, according to an Enel Green Power statement on Tuesday. There was no interruption to local power supply.

An official for the town of Camugnano, located near the site, confirmed the incident in a phone interview. The official said the town’s mayor is at the site to assist along with other local officials and public authorities.

The Bargi plant, which can pump water into the reservoir to balance the grid at times oversupply, is the largest such facility in the central Emilia Romagna region. It can produce 330 megawatts of power, enough to supply about 600,000 average European households.

Enel Green Power Chief Executive Officer Salvatore Bernabei also traveled to the site to oversee operations, according to the statement, as the company works with relevant authorities. 

--With assistance from Daniele Lepido.

(Updates with details on incident, casualities from second paragraph.)

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