Eighteen Indian sailors were trapped and some were killed after an explosion and fire on a diesel-powered submarine at a base in Mumbai Wednesday, souring a week of naval milestones, including the launch of a locally built aircraft carrier.
The explosion just after midnight was likely an accident, but an investigation was under way to establish the cause, navy officials said.
Defense Minister A.K. Antony said crew members inside the Russian-built INS Sindhurakshak had died, but gave no details.
"There are some people who are trapped on board, we are in the process of trying to rescue them," said navy spokesman P.V.S. Satish. "We will not give up until we get to them."
Three people who were near the submarine at the time of the explosion were injured and hospitalized, he said.
Photos distributed by social media users appeared to show a large fireball over the navy dock where the kilo-class diesel-electric submarine was.
"There was a loud explosion post midnight and I woke up," said Dharmendra Jaiswal, who manages a public toilet opposite the naval dockyard. "I could see the skyline was bright and I could make out that some fire or blast had occurred inside."
The incident, the worst ever for the navy's submarine division, drew comparisons to the explosion on the Russian nuclear attack submarine Kursk, which sank to the bottom of the Barents Sea in 2000, killing all 118 crew members.
The Indian vessel, which returned from an upgrade in Russia earlier this year, had suffered a similar accident in 2010 in which one sailor was killed while it was docked in the southern port of Visakhapatnam.
There was no immediate word on the status of the weapons on board the Sindhurakshak.
"Lot of things are in very close proximity, there is fuel, there is hydrogen, there is oxygen, there are weapons with high explosives on board," retired Indian navy chief Arun Prakash told Reuters. "So a slightest mistake or slightest accident can trigger off a huge accident,” he added.
Al Jazeera and Reuters