The oxygen supply in a missing submarine is feared to run out in less than 24 hours.

Rescuers have intensified the search, using underwater sounds to narrow down their hunt.

The US Coast Guard leads the international mission to rescue the five people on board.

Rescue efforts intensified after underwater noises were detected, though their cause remains unknown.

The vessel's oxygen supply is expected to run out on June 22, according to a US Coast Guard spokesperson.

Despite the dire oxygen timeline, officials still consider the operation a "search and rescue mission".

The submarine, named Titan, lost communication while 435 miles south of Newfoundland on a Titanic viewing expedition.

Among the trapped individuals are OceanGate CEO Stockton Rush, French navy veteran PH Nargeolet, and British billionaire Hamish Harding.

The submersible was not safety approved by a regulatory agency, according to an opinion piece by Melanie VanDerveer.

Internet reactions to the crisis have been varied, with comments ranging from empathetic concern to dark humor about the Titanic expedition.