A glimmer of hope has emerged in the effort to find a missing Argentine submarine and its 44 crew members after authorities believe they picked up an attempt to communicate.

The ageing navy sub went missing on Wednesday after it stopped communicating during a routine mission.

Defence officials now believe that seven mysterious blips to a satellite may have been attempts by the crew to communicate.

No contact was apart from the signals, which Argentine searchers say are the first signs of life from the ARA San Juan.

“We received seven satellite calls that likely came from the submarine San Juan. We are working hard to locate it,”  Argentine Defense Minister Oscar Aguad tweeted.

“To the families of the 44 crew members: We hope you’ll have them home soon.”

The longest of the transmissions was just 36 seconds, and while officials could not be certain they were from the stricken ARA San Juan, search leaders believe the German-made submarine is by far the most likely source.

All modern submarines are equipped to release with floating beacons that emit emergency signals via satellite links when exposed to water.

If the mystery signals did come from the San Juan, the storms and heavy cloud over the search area might have stopped them being relayed by the satellite link, officials speculated.

The ARA San Juan was last reported 432km off Argentina’s southern Atlantic coast early on Wednesday, prompting authorities to launch an emergency search-and-rescue operation on Friday.

But a storm with powerful winds and waves six metres high continued to disrupt visibility and efforts to explore Argentine’s southern sea, navy spokesman Enrique Balbi told reporters.

Nevertheless, authorities were renewing their search efforts above and below the surface and were readying an operation to comb the sea floor, said Gabriel Gonzalez, who heads the naval base in the port of Mar del Plata.

The submarine had been headed to Mar del Plata from the city of Ushuaia.

“The underwater search is obviously much more complicated than the search at the surface because it requires a combination of high-tech tools,” Mr Gonzalez told a news conference.

Carlos Zavalla, a navy commander, urged the loved ones of crew members not to give up hope.

“So far, the only concrete thing is the lack of communication,” he said.

Messages of support have poured in from around the world, with Argentine native Pope Francis praying “fervently” for crew members and their families soon, the Vatican announced.

Argentine officials are working on the theory that an electrical outage on the submarine may have caused its communication problems and left the vessel unable to rise to the surface.

-with agencies