All nine persons trapped after a huge fire at an underground hydroelectric power station in Telangana were killed, officials said on Friday.

All the efforts by rescue workers to save the trapped employees at Telangana State Generation Corporation (TS Genco) plant at Srisailam canal's left bank in Nagarkurnool district were futile.

The rescue workers recovered the bodies of five victims. They were identified as Assistant Engineers Mohan Kumar, Uzma Fatima, and Sunder, Divisional Engineer Srinivas Goud and Mahesh, an employee of a battery company.

Efforts were on to trace the bodies of the remaining persons. The rescue personnel including those from the Central Industrial Security Force (CISF) and the National Disaster Response Force (NDRF) were battling thick smoke to retrieve the bodies.

Some rescue workers have also reportedly become ill during the rescue operation.

Earlier, personnel from the NDRF and experts from the Singareni Collieries Company Ltd (SCCL) joined the rescue operations.

The fire, which broke late on Thursday, was brought under control by the firefighters.

A short-circuit is believed to have caused the fire at unit one of the underground power house. Of the 30 persons reported to be present at the spot, 15 escaped to safety through a tunnel while six were rescued by rescue personnel. They were admitted to a local hospital.

One of the survivors said the sparks were first noticed on a panel. "This was followed by series of explosions. There were utter chaos and we all ran out for safety," he said.

Telangana Energy Minister Jagadish Reddy and TS Genco and Transco Chairman and Managing Director Prabhakar Rao rushed to the spot and were overseeing rescue efforts.

Reddy said that the accident occurred in the first unit of the power station and four panels were damaged. He said that rescue personnel were unable to enter the tunnel due to thick smoke.

"As soon as the fire started, they tried to trip the units but that couldn't happen. So we isolated the 400 KV input and all units were tripped," said Prabhakar Rao.

Operations at the power station have been suspended following the incident.

The Srisailam dam is located across the Krishna river which serves as the border between Telangana and Andhra Pradesh.

Telangana Chief Minister K. Chandrashekhar Rao ordered a probe by the CID into the fire.

Following the direction, Chief Secretary Somesh Kumar issued an order appointing Additional Director General of Police, CID, Govind Singh as the inquiry officer. Singh was asked to conduct a comprehensive inquiry and submit the report to the Chief Minister.

The Chief Minister expressed his deep shock over the fire incident and termed it as "very unfortunate". According to a statement from Chief Minister's Office, he voiced his sorrow over the efforts to rescue the trapped people failing to yield results.

KCR, as the Chief Minister is popularly known, conveyed his heartfelt condolences to the families of the deceased. He expressed his best wishes for early recovery of those injured in the incident and directed the officials to ensure best treatment to them. He said the government would bear the entire cost of the treatment.

KCR was in regular touch with Jagdish Reddy and Prabhakar Rao to monitor the situation.

Andhra Pradesh Chief Minister Y.S. Jagan Mohan Reddy, who was scheduled to visit Srisailam on Friday, cancelled his visit in view of the disaster.

Senior officials informed the Chief Minister about the incident and said his visit to Srisailam to participate in pooja and review meetings would not be proper as efforts were on to rescue the trapped employees.

Following this, he decided to cancel his visit. Expressing shock over the fire incident, he assured all support from Andhra Pradesh in the rescue operations.