The U.S. Coast Guard continues searching for a missing submarine that disappeared near the Titanic wreck with five people on board. 

The 21-foot craft, operated by OceanGate Expeditions, began its descent on Sunday but lost contact with the surface less than two hours later, according to authorities. The U.S. Coast Guard said it had launched two planes to survey the remote area in the North Atlantic, while its Canadian counterparts had also sent a plane and a ship.

"It is a challenge to conduct a search in that remote area, but we are deploying all available assets to make sure that we can locate the craft and rescue the people on board," U.S. Coast Guard Rear Admiral John Mauger told reporters in Boston, where he was overseeing the operation.

Time is a critical factor. The vessel has a range of 96 hours for the crew of five, and Mauger said Monday afternoon he believed it still had 70 or more hours of remaining oxygen.

One of the passengers on board has been identified as British businessman Hamish Harding, whose aviation business had posted on social media about his expedition. The 58-year-old chairman of Dubai-based Action Aviation, said on Instagram on Sunday that he was proud to join the OceanGate Expedition for their RMS TITANIC Mission as a mission specialist going down to the Titanic.

"A weather window has just opened up and we are going to attempt a dive tomorrow," Harding wrote.

"The team on the sub has a couple of legendary explorers, some of which have done over 30 dives to the RMS Titanic since the 1980s," he added.

"Our entire focus is on the wellbeing of the crew and every step possible is being taken to bring the five crew members back safely," OceanGate Expeditions' statement said. 

The company uses a submersible named Titan for its dives to a maximum depth of 13,100 feet. The wreckage of the Titanic, which sank in 1912 during its maiden trip from England to New York with 2,224 passengers and crew on board, is located 13,000 feet underwater 400 miles off the coast of Newfoundland, Canada.