Mumbai, Feb 26: Seven Indian Navy personnel were injured and at least two were missing early Wednesday after an accident aboard the INS Sindhuratna submarine that was underwater, official sources said here.

There were 94 sailors onboard the submarine when the accident took place.

The accident – the cause of which is not yet clear – took place in the early hours of Wednesday, about 50 nautical miles (80 km) in the Arabian Sea.

Seven injured sailors were airlifted by helicopter and shifted in an unconscious state to the naval hospital, INS Asvini, in south Mumbai. Two more sailors who were on board the submarine, remain “unaccounted for” or are missing even as a search for them has been launched.

The remaining sailors, including Commodore Commanding Submarine (West) S.R. Kapur, are engaged in the rescue operations currently underway. 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.

Details about what caused the accident were not available, but 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 last December, 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 familiarization 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 and subsequent sinking of the INS Sindhurakshak 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 per cent 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. IANS