Nine people were killed in a fire that broke out at an underground hydroelectric plant in Telangana on Thursday night, ANI reported. All nine people had been trapped inside the plant because of the fire.

Of the 10 people who managed to evacuate when the fire started, six are undergoing treatment at hospitals. Sharma added that thick smoke was still coming out of the tunnel where the plant is situated.

The fire broke out around 10.30 pm on Thursday at one of the power houses inside the plant. Fire engines from the Atmakur Fire Station in Kurnool went sent immediately. A team of the National Disaster Response Force began evacuating those trapped inside the plant, NDTV reported. The Central Industrial Security Force has also joined the rescue operation, according to PTI.

The cause of the blaze is yet to be ascertained. But initial reports point to a short circuit at one of the units of the underground hydroelectric power station.

“Ten people were able to come out,” state Power Minister G Jagadeeshwar Reddy told ANI. “Plant’s power supply was cut off. We’re trying to get help of Singareni Coal Mine, as they might have expertise in such situation. Priority is to rescue the trapped.” Reddy and other top TSGenco officials visited the spot, according to the Hindustan Times. Telangana Chief Minister K Chandrasekhar Rao, meanwhile, ordered a Crime Investigation Department probe into the accident.

Rescue operations have been hampered as the thick smoke engulfed all six units of the power station, reported News18. The rescue personnel reportedly tried to enter the power station units at least three times but were unable to because of the thick smoke.

The Srisailam Left Bank Power Station is a joint irrigation project between Telangana and Andhra Pradesh. It is located on the Krishna river.