The Titanic tourist submersible that vanished on a trip to the 111-year-old shipwreck at the bottom of the Atlantic Ocean is believed to have run out of oxygen — but authorities pushed ahead with the search operation Thursday morning.

OceanGate Expeditions, which operates the Titan sub and whose CEO, Stockton Rush, is aboard the missing vessel, told the Coast Guard on Sunday evening that the vehicle was equipped with only 96 hours of oxygen, with the timer running out around 7:08 a.m. Thursday.

The status of the five passengers aboard the ill-fated trip remains unclear as US and Canadian officials work around the clock to attempt to locate the missing Titan sub 900 miles east of Cape Cod.

The Coast Guard on Thursday morning confirmed that a remote-operated vehicle “has reached the sea floor” and started searching for the missing sub.

“The French vessel L’Atalante is preparing their ROV to enter the water,” it added.

Along with Rush, who served as the vessel’s pilot, the missing include British billionaire Hamish Harding, Pakistani tech and energy mogul Shahzada Dawood and his 19-year-old son Sulaiman, and famed Titanic explorer Paul-Henri Nargeolet.

The US Coast Guard said it received word from OceanGate about the missing submersible eight hours after it lost contact with its mothership, the Polar Prince.

OceanGate said the sub disappeared less than two hours after it submerged Sunday afternoon.

Unlike a normal submarine, a submersible is unable to get to the bottom of the ocean and back without its mothership, with Titan depending on the Polar Prince for navigation in the depths.