An Indian navy submarine with 18 sailors on board has caught fire and sunk at a Mumbai base.

After the fire, the boat became submerged at its berth in the naval dockyard with only a portion visible above the surface.

It is understood the fire was followed by three large explosions.

"The cause of the explosion is not known. We are searching for the 18 personnel," navy spokesman Narendra Kumar Vispute said.

The Russian-made submarine, INS Sindhurakshak, was built 16 years ago and had recently returned from Russia after undergoing an overhaul and upgrade, according to reports.

Navy divers have been trying to rescue the trapped sailors, but so far without success.

There are also unconfirmed reports of missile parts being found on the dockyard.

In February 2010, the INS Sindhurakshak also suffered a fire while docked in Visakhapatnam city in southern India, killing a sailor (24) and leaving two others with burns.