The submarine was in dock when the explosion took place and it’s thought the missiles and torpedoes inside may have detonated as well.
It took rescue workers more than two hours to put out the fire that followed the explosion and divers have not been able to reach the wreck to check for survivors.
There were 18 members of the Indian Navy on-board and all are feared dead.
The sub was obviously older and reports say it was missing up to date safety gear. "They don't have escape routes in the event of accidents, unlike some of the modern submarines," a defense worker told AFP.
Reports say India bought the 16 year old diesel sub INS Sindhurakshak from Russia last year for $80 million.
It isn’t the first time this vessel has had issues. In 2010 a sailor was killed in a fire on-board.