The Argentine navy is concerned that the oxygen supplies of ARA San Juan submarine that went missing may be running low, said Captain Enrique Balbi, a navy spokesman.

“It’s already an extreme situation, since today is the sixth day without the replenishment of oxygen reserves,” Balbi said on Wednesday,” according to BBC. “We are gradually nearing the extreme threshold.”

The first reports on the disappearance of this submarine were received on November 17.

According to Telesur pan–Latin American television, the search team in the Atlantic Ocean on Wednesday recorded a danger signal, which probably came from the vanished submarine.

There are 44 crew on board the ARA San Juan, which is under the command of Pedro Martín Fernández.