Relatives of Argentinian sailors missing after their submarine lost contact in the South Atlantic have reacted with shock after the country's navy revealed the vessel may have exploded.

The abnormal and violent sound was recorded around the time that the submarine sent its last signal and in the same area

Key points: The noise was detected shortly after submarine lost contact

The noise was detected shortly after submarine lost contact Ships and aircraft are continuing search

Ships and aircraft are continuing search Some relatives of crew members lash out at navy

US and specialist agencies said the "hydro-acoustic anomaly" was produced just hours after the navy lost contact with the submarine, which had 44 crew on board, on November 15.

Navy spokesman Enrique Balbi said evidence showed "an anomalous event that was singular, short, violent and non-nuclear that was consistent with an explosion".

"According to this report, there was an explosion," Mr Balbi told reporters.

"We don't know what caused an explosion of these characteristics at this site on this date."

The ARA San Juan had only enough oxygen to last seven to 10 days if submerged. ( Argentina Navy )

But he said the search would continue until there was full certainty about the fate of the ARA San Juan, which has been missing for nine days.

The implosion of a submarine that falls deeper than its "crush depth" would make such a sound, according to one former US navy captain.

Argentine navy ships as well a US P-8 Poseidon aircraft and a Brazilian air force plane are returning to the area to check out the abnormal sound, which originated about 50 kilometres north of the submarine's last registered position.

Boat had been cut in half in 2014

Relatives of the crew who have gathered at the base to receive counselling broke into tears and hugged each other after they received the news.

Some declined to speak, while others lashed out in anger at the navy's response.

"They sent a piece of crap to sail," said Itati Leguizamon, wife of submarine crew member German Suarez.

"They inaugurated a submarine with a coat of paint and a flag in 2014, but without any equipment inside.

"The navy is to blame for its 15 years of abandonment."

Relatives gathered at the Mar del Plata Navy Base break into tears upon hearing the news. ( Reuters: Marcos Brindicci )

The German-built diesel-electric TR-1700 class submarine was commissioned in 1985 and was most recently refitted in 2014.

During the $16 million retrofitting, the vessel was cut in half and had its engines and batteries replaced.

Experts say that refits can be difficult because they involve integrating systems produced by different manufacturers and even the smallest mistake during the cutting phase of the operation can put the safety of the ship and the crew at risk.

Searchers head for area where sound was detected

The Argentine navy and outside experts had said that even if the ARA San Juan was intact, its crew might have only enough oxygen to be submerged for seven to 10 days.

The search location straddles the edge of the continental shelf, with widely varying ocean depths, some as great as 3,000 metres.

Experts say the submarine could not have supported pressures that far down.

"If a submarine goes below its crush-depth, it would implode, it would just collapse," said James H Patton Jr, a retired navy captain.

"It would sound like a very, very big explosion to any listening device."

Whatever it was, US Navy Lieutenant Lily Hinz said the sound detected "was not a whale, and it is not a regularly occurring sound".

The San Juan lost contact as it was sailing from the extreme southern port of Ushuaia. The submarine's captain had reported a battery failure.

The sub had been heading for the Mar del Plata Navy Base, about 400 kilometres south-east of Buenos Aires.

Map of Argentina's San Jorge Gulf, the submarine's last known location.

ABC/AP