All the nine people, trapped in the Srisailam hydroelectric plant on the Telangana-Andhra Pradesh border where a fire broke out, died, a senior government official said.
Six bodies have been recovered by rescue teams so far, and efforts were on to pull out the others from the underground plant, Nagarkurnool district collector L. Sharman said.
The fire broke out late on Thursday night when at least 17 people were inside the plant and eight of them managed to come out, officials said.
Chief Minister K. Chandrasekhar Rao, who had expressed shock over the incident, ordered a comprehensive probe by the Crime Investigation Department (CID) into the incident.
According to media reports, the chief minister said all efforts were made to rescue those trapped inside, but in vain.
Energy Minister G Jagdishwar Reddy said fire and the rescue personnel made several unsuccessful attempts to go in and rescue those trapped. "Despite having oxygen cylinders, they found it difficult to enter the place," the minister was quoted as saying.
Preliminary reports suggest that the fire was caused by a short circuit.
Though the fire was put off, thick smoke engulfed the tunnel where the power plant is located, hampering the rescue operations.
Built on river Krishna, the Srisailam Left Bank power station, about 200 km from Hyderabad, is operated by the Telangana State Power Generation Corporation (GENCO).
The plant has six units with combined capacity of 900 MW (6X150). The power generation was in full swing following the incessant rains during the past few days. Power generation has been suspended following the fire mishap.
(With PTI inputs)