Hambantota Port in Sri Lanka built by China

Presence of nearly 3,000 "dark ships" in the vast expanse of the Indian Ocean at any point in time is the cause of a new worry for the Indian Navy.

These are vessels that either don't have the automated identification system (AIS) or don't switch it on despite having the instrument on board.

In the absence of the AIS, the surveillance units are in the dark of the nature of these vessels, their cargo and the routes.

"Dark shipping" adds a new security concern in the strategically important Indian Ocean, where the enhanced presence of Chinese warships and submarines as well as thousands of fishing boats already pose a big security challenge.

"Globally, there are an estimated 22,000-30,000 dark vessels, out of which nearly 3,000 are in the Indian Ocean. Dark shipping is on the rise, but these vessels are not on our radar," a senior official in the security establishment told DH.

The navy plans to boost its surveillance network with a new and powerful software where multiple data inputs would be fed by 38 more coastal radars, white shipping information from other countries, satellites and reconnaissance aircraft in addition to the existing sources.

India experienced the dangers of dark shipping almost five years ago when a floating armoury (MV Seaman Guard Ohio) was intercepted by Indian authorities in October 2013, off Tuticorin, with 25 armed guards of four different nationalities.

Sources said nearly 140 private security companies were operating in the north Indian Ocean.

They hire private armed security personnel, who shift between the vessels on the high sea.