A NASA research plane has joined the search for a missing Argentine submarine, as concern is growing over the fate of its 44 crew members.

No contact has been made with the vessel, the ARA San Juan, since Wednesday, prompting authorities to launch a major air and sea search operation.

"We will do what is necessary to find the submarine as soon as possible," President Mauricio Macri said on his Twitter account on Saturday.

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.

Argentina accepted an offer from the United States for a NASA P-3 explorer aircraft, which had been stationed in Ushuaia and was preparing to depart to Antarctica, to make an exploratory flight over the search area.

Rising tension

Al Jazeera's Daniel Schweimler, reporting from Mar Del Plata, said "tension is mounting" with "each hour that goes by".

"The families of those crew members are gathering at the naval base here in Mar Del Plata," said Schweimler, adding that Pope Francis - an Argentine - had said he was praying for the missing crew members.

The German-made ARA San Juan is one of three submarines in the Argentine fleet.

"It is a very old submarine," said Schweimler.

"The Argentines bought it second-hand from its German manufacturers back in 1985. It had a big overhaul in 2008 with the idea of it staying in service for another 30 years."