No contact has been made with the Argentine submarine, the ARA San Juan for the last 72 hours and an extensive air and sea search operation is underway with assistance from the US and UK.
A Nasa research plane as well as a U.S. Navy P3 has joined the search for the vessel.
The TR-1700 class diesel-electric vessel had been returning from a routine mission to Ushuaia, near the southernmost tip of South America, to its base at Mar del Plata, around 400km south of the capital, Buenos Aires.
The German built submarine was commissioned in 1983.