NEW DELHI – The situation looked bleak late Wednesday after an explosion and fire on an Indian submarine left three officers and 15 sailors trapped inside, and navy divers failed to make contact or discern sign of life coming from inside the stranded vessel, officials said.

The explosion occurred about 12:30 a.m. Wednesday leaving the diesel- and electric-powered submarine largely submerged at a dock in Mumbai where it was berthed, the navy said.

Grainy social media footage showed a huge white and yellow explosion illuminating the midnight sky like a premature dawn, followed by a blaze that lasted several hours. The base where the accident took place is a secure area off-limits to reporters.

“We should hope for the best, but be prepared for the worst,” Adm. Devendra Kumar Joshi, chief of the naval staff, told reporters at a news conference in Mumbai.

“The explosions were massive and we’ve had no contact with any of the sailors. They are missing for more than 12 hours now.”

Defense Minister A.K. Antony told reporters in New Delhi that several crew members died, without providing details. “It is the greatest tragedy of recent times,” he added.