18 trapped after Indian submarine explodes and sinks in Mumbai

A Russian-built submarine of the Indian navy has exploded in Mumbai harbour, with 18 sailors believed to be trapped inside.

Several other crew members were reported to have escaped by jumping off the submarine when it blew up on Tuesday night, sparking a huge fire. Several injured navy personnel were being treated in a naval hospital.

"Naval divers are trying to rescue the sailors still inside the semi-submerged submarine," said naval spokesman PVS Satish. "We will not give up until we find them."

After the explosion in the Russian Kilo-class INS Sindhurakshak, two torpedoes from the submarine were set off, damaging other vessels in the naval dockyard.

India's defence minister AK Antony confirmed that people died when a navy submarine caught fire and sank at its home port in Mumbai. He gave no details. "I feel sad … about those navy personnel who lost their lives in the service of the country," Antony told reporters outside parliament in New Delhi.

The diesel-electric submarine, built in St Petersburg in 1997, had undergone a two-year upgrade in Russia after a battery on board gave trouble in April 2010.

Capable of firing cruise missiles at a range of 125 miles (200km), it had been reintroduced into the Indian navy only in April.

The explosion is believed to be an accident, and investigations are likely to focus on the same cause as in 2010 – a defective battery.

Social media film of the explosion, repeatedly aired on Indian TV networks, showed a huge ball of fire lighting up the naval dockyard in Mumbai.

Besides navy firefighting units, 16 fire engines from the Mumbai Fire Brigade battled the inferno, which was brought under control at around 3am.

According to TV news reports, the fire set off two torpedoes on board the INS Sindhurakshak, and the deadly missiles hit another submarine and a naval vessel. The damage to the second submarine was minor, the reports suggested.

"It's a major setback, as out of around 14 submarines, the Indian navy only has a few operational subs available," said Srinjoy Chowdhury, defence correspondent of Times Now. "The INS Sindhurakshak was one of them."

The Indian navy had been celebrating two breakthroughs in the past week in its quest to emerge as a "blue-water navy", capable of operating across vast stretches of ocean.

Its first home-built aircraft carrier, INS Vikrant, was launched on Monday, though it will not be battle-ready until 2020. And on 10 August the reactor in India's first indigenously built nuclear submarine, INS Arihant, went critical.

The nuclear-powered submarine is due to begin sea trials before it is made fully operational. The navy already has on lease a Russian-built nuclear submarine, the INS Chakra. But the Chakra cannot be armed with nuclear-tipped missiles due to international non-proliferation treaties.