New Delhi (CNN) -- Navy divers have recovered five bodies so far from an Indian navy submarine that exploded and sank in Mumbai this week, authorities said Saturday.
The Indian government warned that there was almost no hope of finding any survivors among the 13 other sailors who were in the submarine when it was hit by the unexplained blast at a naval dockyard early Wednesday.
Navy divers searching the trapped submarine for three days have recovered five bodies so far.
Their task has been complicated by poor visibility inside the stricken submarine's passageways, which are full of oily, muddy water and wreckage. Adding to their difficulties, the heat of the explosion warped some of the hatches inside the vessel, blocking the divers' access to certain areas.
The bodies found so far are unidentifiable because they were so severely burned, authorities said. They have been taken to a naval hospital for DNA identification.
Searching 'every inch'
The state of the bodies and conditions inside the INS Sindhurakshak, a Russian-built submarine, mean that "finding any surviving personnel within the submarine is unlikely," the ministry said.
"The feasibility of locating bodies of personnel in the forward part of the submarine is also very remote, as the explosion and very high temperatures, which melted steel within, would have incinerated the bodies, too," it warned.
But divers will scour through submarine until all the bodies are recovered, the ministry said.
Authorities say they have contacted the families of all the 18 missing personnel and are keeping them updated.
Worst peacetime disaster
An investigation into the explosion and fire -- the Indian navy's worst peacetime disaster -- is under way. Navy officials say they so far can't pinpoint the cause.
Salvage work on the diesel-electric submarine won't begin until the search for bodies is over, the defense ministry said.
The Sindhurakshak had recently returned from an extensive refitting in Russia before the disaster.
CNN's Harmeet Shah Singh reported from New Delhi, and Khushbu Shah from Atlanta.