The deadly explosion aboard an Indian submarine with 18 sailors on board is the worst loss for the country's navy since its 1971 war with Pakistan, and is seen as a setback to India's modernization of its defense capabilities.
"I am saddened by those naval personnel who lost their lives in the service of the country," said Defense Minister A.K. Antony. "It is a great tragedy for the navy."
Officials said there has been no contact with any of the sailors since the explosion.
Wednesday's blast aboard the submarine, INS Sindhurakshak, which was berthed at a Mumbai dockyard, comes a day ahead of Independence Day celebrations in the country.
The explosion lit up the sky, and the blaze could be seen in different parts of the city. Defense officials ruled out terrorism as a possible cause. Recovery efforts are underway.
The explosion comes days after two breakthroughs for India's navy: On Sunday, the country powered up the reactor on its first locally made nuclear submarine. A day later, it unveiled its first homemade aircraft carrier.
The Russian-made submarine was delivered to India in 1997. It was one of 10 Kilo-class submarines — known in India as Sindhughosh class — that India bought from Russia between 1986 and 2000.
A previous fire aboard the INS Sindhurakshak's battery compartment in February 2010 killed one sailor. The sub was sent to Russia later that year for a refit. The refurbishing of the sub, now outfitted with cruise missile systems, was completed in June 2012, adding at least a decade to its life.
NPR's Julie McCarthy, reporting on the blast on Morning Edition, said the explosion was reminiscent of the blast aboard Russia's Kursk submarine, which sank in 2000 following an explosion that killed all 118 sailors on board.
The Associated Press notes that Wednesday's accident comes as India faces a shortage of submarines because of obsolescence:
"The government has authorized the navy to have up to 24 conventional submarines, but it has just 14, including eight Russian Kilo-class and four German Type HDW209 boats. [Rahul] Bedi [an analyst for the independent Jane's Information Group] said five of those will be retired by 2014-15.
"Last year, India acquired a Russian Nerpa nuclear submarine on a 10-year lease at a cost of nearly $1 billion. India also has designed and built its own nuclear submarine. The navy activated the atomic reactor on that vessel on Saturday and could deploy it in the next two years.
"India has steadily built up its naval capabilities in recent years, spurred by its rivalry with neighboring China. But the country's military has encountered scandal as it attempts to bulk up."
India lost a brief but bitter border war to China in 1962.