Time is running out to find the missing submarine, which only has a few more days of air.
A US navy plane searching for a missing Argentinian submarine has spotted an object on the ocean floor, local media say.
The plane's radar had discovered an area of heat around 70m below the surface of the southern Atlantic, leading rescuers to believe it could be the missing ARA SanJuan, the radio station Mitre and the newspaper Clarin reported.
A mini submarine had been sent to the spot, 300km east of the Patagonian harbour Puerto Madryn, to identify the object, they reported. Argentina's Ministry of Defence refused to confirm the report.
The German-made submarine, with 44 crew members on board, went missing six days ago. It has a seven-day supply of oxygen.
Comandante Espora Argentine ship sails off the naval base in Mar del Plata at the weekend. The ship is is part of a crew searching for the missing submarine. Photo / AP
The regional hospital in the city of Comodoro Rivadavia has been ordered to prepare for possible casualties, with all operations cancelled and four theatres freed up.
The search operation, which has 13 planes and 17 boats at its disposal, is now at a "critical phase," according to the Argentinian navy.
"Our concerns about the oxygen reserves on board are growing," navy spokesman Enrique Balbi said.
The search is the largest manoeuvre in the southern Atlantic since the Falklands War of 1982, covering 482,000 square kilometres.
Hopes had been raised and dashed earlier after the sighting of a lifeboat and flares proved to be false alarms, as did a noise detected coming from the ocean.
Family members of the crew who are gathered at the Mar del Plata naval base are increasingly distressed, navy psychologist Victor Hugo Duga said.
A priest holds a rosary as he prays with family members of the 44 crew members of the missing Argentine submarine ARA San Juan, outside the Mar del Plata Naval Base yesterday. Photo / AP
"The state of mind is very low," he said.
In its last contact with its naval base last Wednesday, the submarine had given word of a battery glitch, Captain Gabriel Galeazzi, another navy spokesman, said.
The crew was then ordered to take the shortest route to its home port of Mar del Plata, 400km south of Buenos Aires, Galeazzi said.
The navy has avoided associating the mechanical problem with the disappearance of the vessel and said it had sufficient back-up machinery.
