The submarine was last heard from Wednesday from the southern Argentine sea, 268 miles from the Patagonian coast. It was headed to the coastal city of Mar del Plata in Buenos Aires province, Reuters reported.
Navy spokesman Enrique Balbi told Reuters the operation was officially upgraded to search-and-rescue status Friday. But poor weather conditions have made it difficult for the Navy to locate the missing vessel, Reuters reported.
The P-8A Poseidon is expected to aid in the search because its technology allows it "to support a wide range of missions over large bodies of water, including sub-surface search-and-rescue operations," a Navy statement said.
The U.S. also has offered to fly the NASA P-3 explorer aircraft to help in the search, Reuters reported.
Other countries offering assistance include Brazil, Uruguay, Chile, Peru, United Kingdom and South Africa.
"We share their concern and that of all Argentines," President Mauricio Macri tweeted, according to Reuters. "We are committed to using all national and international resources necessary to find the ARA San Juan submarine as soon as possible."