Billionaire businessman who traveled to space with Jeff Bezos’s Blue Origin among group missing on Titanic submarine voyage
Fortune · Victoria Sirakova—Getty Images

Search efforts to locate a missing submarine with five people on board in the depths of the north Atlantic are continuing frantically, as oxygen supplies are reported to be rapidly depleting.

The Titan submersible was taking tourists to see the wreckage of the Titanic, which famously sank in 1912 on its maiden voyage from Southampton, England, to New York City.

The submersible went missing on Sunday, 700 kilometers (435 miles) off the coast of Newfoundland, Canada. Contact was lost with the crew an hour and 45 minutes into its dive.

OceanGate, the company operating the dive, said in a statement on Monday that it was “exploring and mobilizing all options to bring the crew back safely.”

“Our entire focus is on the crew members and their families,” the company said, before thanking the government agencies and deep-sea companies assisting with the search.

Tickets for OceanGate’s Titanic expeditions reportedly cost $250,000 each, with the dives reaching a maximum depth of 3,800 meters (12,500 feet). The missions are supposed to last for 10 days, eight of which are spent at sea.

The U.S. Coast Guard said Monday it was working with Canadian authorities to conduct a search of the area where the sub disappeared, and that aerial searches, surface vessels, and sonar were being used in the recovery mission.

The Coast Guard estimated on Monday that the Titan had between 70 and 96 hours of emergency oxygen available.

According to OceanGate’s website, the Titan is stocked with 96 hours of “life support” for five crew members.

On Tuesday, Sky News reported that a NATO rescue sub was not able to reach the depths required to find the Titan—and that a waiver passengers are required to sign before participating in the Titanic dive “mentions death three times.”

Who’s on board the missing sub?

British billionaire Hamish Harding, chair of private jet company Action Aviation, is among those aboard the submersible.

Harding said on social media on Saturday that over the coming days, he would be making the journey into the depths of the ocean to see the Titanic wreckage—and pointed out that treacherous weather conditions may mean that the entire dive would have to be called off.

On Sunday, Action Aviation announced via Twitter that the RMS Titanic Expedition Mission 5 had begun at 4 a.m. local time that day.

“The sub had a successful launch, and Hamish is currently diving,” the company said, before promising “further updates” as the mission progressed.