A search and rescue mission was underway Monday for a submarine that went missing in the North Atlantic on an expedition to explore the wreckage of the Titanic. Lt. Jordan Hart of the U.S. Coast Guard in Boston first confirmed to CBS News that personnel were "currently undergoing a search and rescue operation" when asked about the rescue efforts off the coast of Newfoundland. 

At a news conference Monday afternoon, Rear Admiral John Mauger confirmed that five people were aboard. A Coast Guard official identified them as an operator and four mission specialists — a term the company uses for its passengers.

The vessel submerged on a dive Sunday morning, and the crew of the Polar Prince — the ship that ferried the submersible and expedition members to the dive site — "lost contact with them approximately 1 hour and 45 minutes into the vessel's dive," the Coast Guard said in a tweet. 

OceanGate Expeditions, a company that deploys manned submersibles for deep sea expeditions, confirmed in a statement that its sub was the subject of the rescue operation, adding that it was "exploring and mobilizing all options to bring the crew back safely."

The company did not say whether any of the people on board are paying tourists. It takes them as passengers on its expeditions. 

"Our entire focus is on the crewmembers in the submersible and their families," said OceanGate, adding that it was "deeply thankful for the extensive assistance we have received from several government agencies and deep sea companies in our efforts to reestablish contact with the submersible." 

The U.S. Coast Guard said it had a C-130 crew searching for the sub approximately 900 miles off Cape Cod, and that the Rescue Coordination Center Halifax is assisting with a P8 Poseidon aircraft, which has underwater detection capabilities. Aircraft are searching from above while vessels also search on the water, Mauger said at the briefing. Sonar buoys have been deployed in the water in an attempt to listen for the missing sub. They're capable of listening to a depth of 13,000 feet.

"It is a remote area and 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," Mauger said. 

The Coast Guard is also working with military and civilian partners to develop a rescue plan if the vessel is located underwater, Mauger said. 

"Right now we're focused on locating the vessel. But at the same time, if we find this vessel in the water then we will have to effect some sort of rescue," Mauger said. "We're coordinating, reaching out to different partners within the U.S. Navy, within the Canadian armed forces, and within private industry to understand what underwater rescue capability might be available."

The sub is believed to have a 96-hour sustainment capability if there's an emergency on board.

"We're making the best use of every moment of that time to locate the vessel," Mauger said.

Asked about the emergency oxygen supply, Mauger said, "We anticipate that there are somewhere between 70 to the full 96 hours available at this point."

The Coast Guard first alerted mariners Sunday night that a "21 foot submarine" with a white hull was overdue, giving its last known position. "VESSELS IN VICINITY REQUESTED TO KEEP A SHARP LOOKOUT, ASSIST IF POSSIBLE," the message said.

Contacted by CBS News, the Canadian Coast Guard said the rescue operation was being managed by the Boston Regional Coordination Center, and a map showing jurisdictions for the various coastal search and rescue agencies off the North American coast shows the location of the Titanic wreck within the Boston center's area of responsibility.  

OceanGate recently said on its website and social media feeds that an expedition to the wreckage of the RMS Titanic, which lies about 400 miles southeast of the Newfoundland coast, was "underway." 

The company last tweeted about the Titanic expedition on June 15.

On Saturday, British businessman Hamish Harding shared on Facebook that he was among the group on the OceanGate expedition that had departed from St. Johns, Newfoundland, the day before. "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," Harding wrote. He said it was "likely to be the first and only manned mission to the Titanic in 2023" due to weather conditions, and that the team planned to start dive operations at around 4 a.m. Sunday.

Mark Butler, managing director of Harding's company, Action Aviation, told The Associated Press, "There is still plenty of time to facilitate a rescue mission. There is equipment on board for survival in this event. We're all hoping and praying he comes back safe and sound."

Richard Garriott de Cayeux, president of The Explorers Club, said in a letter to the club's members that, "When I saw Hamish last week at the Global Exploration Summit, his excitement about this expedition was palpable. I know he was looking forward to conducting research at the site." Harding helped found the club's board of trustees. The club, which was started in 1904, describes itself as " a multidisciplinary, professional society dedicated to the advancement of field research, scientific exploration and resource conservation." 

Harding, a veteran adventure tourist, had traveled to space aboard a Blue Origin rocket last year.

The Dawood family, of the Dawood Group, a Pakistan-based multi-faceted global conglomerate, issued a statement Tuesday saying, "Our son Shahzada Dawood and his son, Suleman" are on the expedition.

"We are very grateful for the concern being shown by our colleagues and friends and would like to request everyone to pray for their safety while granting the family privacy at this time," the statement said.

The California-headquartered Seti Institute says "Shahzada Dawood is Vice Chairman of Dawood Hercules Corporation, part of the Dawood Group, which has been a family business for over a century."

Diver and explorer Rory Golden also posted about being on the Titanic expedition. In a Facebook post Monday afternoon, he wrote: "I'm OK. We are all focussed on board here for our friends."

He continued: "We have a situation that is now the part of a major Search and Rescue effort, being undertaken by major agencies. That is where our focus is right now. 

"The reaction and offers of help globally is truly astonishing, and only goes to show the real goodness in people at a time like this." 

OceanGate's submersible, The Titan, is the only five-person sub in the world capable of reaching the Titanic wreck, which sits about 2.4 miles below the sea surface. CBS News "Sunday Morning" correspondent David Pogue joined the crew of the vessel, along with a small group of intrepid tourists, for a journey to see the world's most famous shipwreck last year.  

As he got situated in the vessel, which he said had about as much room inside as a minivan, Pogue said he "couldn't help noticing how many pieces of this sub seemed improvised, with off-the-shelf components," including a video game controller that was used to pilot the sub.

On Monday, following news of the missing sub, Pogue tweeted about how the vessel "got lost for a few hours LAST summer, too, when I was aboard," including a link to watch that portion of his video piece on YouTube.

Miles Doran contributed to this report. 

In:
• North Atlantic
• Shipwreck
• Rescue
• RMS Titanic
• Submarine
• United States Coast Guard
• OceanGate
• Canada