MUMBAI, (AFP) -- Indian navy divers have entered a stricken submarine which exploded and sank Wednesday in Mumbai but have detected no signs of life from the 18 crewmen on board, the navy said.

Asked if there had been any communication with survivors, chief of naval staff D.K. Joshi told a press conference: "Of course not. I would have said so if we had."

He added: "There is a possibility of an air pocket. Whilst the indicators are negative, one cannot lose hope."

Joshi added that divers had entered the vessel through the main hatch and would begin pumping out the water to try to float the submarine to the surface.

Initial indications were of a "primary explosion of a minor intensity which caused a bigger explosion" when some of the weapons on board ignited, he said.

"The basic question is what caused the fire and explosion. We do not have an answer to that question as of now."

A board of enquiry established by the navy would probe all possible explanations for the initial fire including sabotage, but "the indicators at this point of time do not support that theory", he said.