The first of six Scorpene attack submarines being built in India by Mazagon Docks Ltd has taken to water as it enters an advanced stage of completion.

The Sunday Guardian reported the vessel is now on schedule to be delivered to the Indian Navy in September of next year, with the remainder of Scorpenes being handed over at nine-month intervals.

"Both the pressure and the outer hull of the first Scorpene are in place," an unidentified Indian Navy source told the newspaper. "Much of the internal fit is also progressing well.

"The submarine will now be placed on a pontoon, and tugged out of MDL docks to the nearby Indian Navy Dock. This will free one precious submarine-building dock at MDL, and thus help in meeting deadlines for subsequent Scorpenes."

The Scorpene is a French-designed submarine from DCNS, which is transferring technology to Mazagon Docks Ltd under an agreement with Indian authorities.

Delivery of the first Scorpene to the Indian Navy is scheduled for September 2016. Thereafter, the delivery of the subsequent five has been promised at the rate of one every nine months.

The Indian Navy plans to arm the diesel-powered submarines with Exocet missiles and Black Shark torpedoes.

The newspaper described the construction of the submarines as a "desperately needed relief for the Indian Navy, which has lost five submarines in the last 15 years due to decommissioning or phase-out and accident, but not added a single new conventional submarine.