Indian navy divers have entered a crippled submarine hit by twin explosions but have yet to reach any of the 18 sailors who are feared dead inside the vessel, a naval official said Thursday. The Russian-built submarine had also been damaged in a deadly explosion in 2010 and had only recently returned to service.

The official, speaking on condition of anonymity because he was not authorized to speak to the media, said water was being pumped from the flooded, diesel-powered submarine so it could be raised completely to the surface. It is currently partially submerged at a dock in a Mumbai navy base, with a portion visible above the waterline.

He said there had been no contact with the sailors since the explosions, which lit up the sky above the base. The official said there appeared to be no way the sailors could have survived the intensity of the blasts and fire.

"We hope for the best but we have to prepare for the worst," Admiral D.K. Joshi, the navy chief, told reporters Wednesday earlier in Mumbai.

Blast in torpedo compartment

The explosions in the submarine's torpedo compartment sent a huge fireball into the air and sent nearby sailors jumping into the sea in panic. It is shaping up to be another embarrassment for India's military, which has been hit with a corruption scandal as it races to modernize its forces.

Because the submarine was docked, navy watchmen were on the submarine rather than the normal crew, Joshi said. At least some weaponry exploded in the near-simultaneous blasts, he added.

A video of the explosions filmed by bystanders showed an enormous ball of red and yellow fire rising hundreds of feet into the air. About a dozen fire engines rushed to the dockyard and extinguished the fire in about two hours, officials said.

Navy spokesman Narendra Vispute said the cause of the explosions was being investigated.

The 16-year-old Russian-made submarine, INS Sindhurakshak, was hit by an explosion in 2010 that killed one sailor and injured two others. The navy said that accident was caused by a faulty battery valve that leaked hydrogen, causing an explosion in the vessel's battery compartment.

The sub recently returned from Russia after a 2 1/2 year refit, overhaul and upgrade, said Rahul Bedi, an analyst for the independent Jane's Information Group. Joshi, the navy chief, said it returned to India in April, and had been certified for use by the Indian navy.

Russian ship repair company Zvyozdochka said the blasts were unrelated to its repair work.

"According to the members of our warranty group, the vessel was functioning properly and had no technical faults at the time of the incident," the Interfax news agency quoted an unidentified company representative as saying.

Zvyozdochka said the submarine had been "in active use" and had logged 24,000 kilometres on three missions.

Facing sub shortage

Wednesday's accident came at a time when India is facing a shortage of submarines because of obsolescence, Bedi said.

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. Bedi 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 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.

In February, India put on hold a $750 million deal to buy helicopters from Italian aerospace and defense giant Finmeccanica and its British subsidiary, AgustaWestland, following charges of kickbacks and bribes. Three of the 12 helicopters were delivered in December and the rest have been put on hold.

Giuseppe Orsihe, the former head of Finmeccanica, is facing trial in Italy for his alleged role in the payment of bribes to secure the helicopter contract.