Seven Indian Navy personnel were injured and at least two went missing Wednesday after smoke filled a compartment in the INS Sindhuratna submarine that was underwater, official sources said here.
There were 94 sailors on board the submarine when smoke was reported in the sailors' accommodation early Wednesday, about 50 nautical miles (80 km) in the Arabian Sea.
Seven sailors were airlifted by helicopter and shifted in an unconscious state to the naval hospital, INS Asvini, in south Mumbai. Their condition is reported to be stable.
Two more sailors who were on board the submarine, remain "unaccounted for" or are missing and a search for them has been launched.
The remaining sailors, including Commodore Commanding Submarine (West) S.R. Kapur, are engaged in the rescue operations. Kapur is in-charge of all the submarines under the Western Naval Command here.
Officials suspect that the two "unaccounted for" officials may have been trapped in one of the sealed compartments of the vessel.
A Western Naval Command release said the submarine was "at sea off Mumbai for routine training and workup (inspection)".
"While at sea in the early hours of Feb 26, 2014, smoke was reported in the sailors' accommodation, in compartment No.3, by the submarine. Smoke was brought under control by the submarine's crew," it said.
The release said that in the process of controlling the smoke, seven crew members inhaled smoke "and felt uneasy".
A helicopter with medical team was sent and the seven crew members were transferred to naval hospital INS Asvini in Mumbai.
"All specialist medical officers attended and reported that the crew is safe. Naval ships were dispatched by HQWNC (Headquarters, Western Naval Command) and are in the area to provide assistance to the submarine. Two personnel have not yet been located and all efforts are in progress to locate them," the release said.
It said all other crew of the submarine "are on board and safe".
The submarine was safe and did not have any weapons on board. It was scheduled to return to harbour in the evening, the defence ministry statement said.
Preliminary reports suggest that the toxic smoke may have been caused either due to a fire or a leakage in one of the hydrogen batteries on the vessel.
Refitted and renovated in Mumbai in December 2013, the INS Sindhuratna was on a training exercise to familiarize the crew with operations of the Russian-built vessel.
The vessel was underwater at the time of the incident and it was not fitted with weapons of any kind as it was on a training and familiarisation mission.
The Indian Navy has ordered an inquiry into the incident - the tenth in recent times - which has hit its elite fleet of submarines.
The biggest accident involved the fire on the INS Sindhurakshak and the subsequent sinking of the submarine in the Mumbai harbour Aug 14 last year, killing all 18 personnel aboard.
Defence Minister A.K. Antony earlier this month expressed concern over the accidents suffered by the navy over the past few months.
Antony said that even one accident was "serious" for him and there was need to strictly follow standard operating procedures and draw proper lessons.
He also said he cannot give the navy "100 percent satisfaction certificate".
There have been a string of navy accidents.
INS Talwar, a frigate, collided with a fishing vessel last year.
A fire broke out on INS Konkan at the dry dock in Visakhapatnam in December 2013 when it was in the dry dock for maintenance.
And INS Betwa, also a frigate, suffered damage in January.
INS Vindhyagiri, a Nilgiri class frigate, sank after it caught fire when it collided with a merchant vessel near the Mumbai harbour in 2011.
