(CNN) — Officials are in a race against time to find a civilian submersible that had five people aboard after it went missing Sunday in the North Atlantic while voyaging to the wreckage of the Titanic.

The 21-foot vessel has four days of emergency capability, the leader of search and rescue efforts said Monday afternoon, as crews with the US and Canadian coast guards continued scouring the ocean’s surface about 900 miles east of Cape Cod and used sonar to listen for sounds far below the water, which is up to 13,000 feet deep in the area.

The five people on board the vessel, which was on an expedition to view the Titanic wreckage, comprised one pilot and four “mission specialists,” Rear Adm. John Mauger, commander of the US Coast Guard’s First District, said Monday in a news conference. He didn’t identify the five and said authorities still were in the process of contacting family members.

He referred reporters to the group conducting the expedition, OceanGate Expeditions, for information about what the term “mission specialist” entails.

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“We’re working very closely at this point to make sure that we’re doing everything that we can do to locate the submersible and rescue those on board,” Mauger said.

The Canadian research ship Polar Prince on Sunday notified the military branch it had lost contact with the underwater vessel, according to Coast Guard spokesperson Lt. Samantha Corcoran. In a tweet, the Coast Guard said the communication stopped approximately 1 hour, 45 minutes into the vessel’s dive.

Time is a factor, officials said. “In terms of the hours, we understood that that was 96 hours of rescue or emergency capability from the operator,” Mauger told reporters. “And so we anticipate that there’s somewhere between 70 to the full 96 hours available at this point.”

A British businessman based in the United Arab Emirates, Hamish Harding, is one of the people on the submersible, according to a social media post by the company he owns, Action Aviation.

“The sub had a successful launch and Hamish is currently diving,” the company said in an Instagram post on Sunday.

Harding was one of the first people to travel the Challenger Deep in the Pacific Ocean – the deepest known point on Earth. On Saturday he wrote of the Titanic mission: “I am proud to finally announce that I joined OceanGate Expeditions for their RMS TITANIC Mission as a mission specialist on the sub going down to the Titanic.”

Search assets include civilian ships

C-130 aircraft were searching the surface and two P-8 planes that use sonar to find submarines were part of the search efforts, Mauger said Monday. Commercial ships are also involved and one has sonar, he added.

“Oftentimes, we rely on commercial operators to be the first vessels on scene,” Mauger said. “And so we’ve been in touch with additional commercial vessels that are operating in the area as well as initiating the movement of additional Canadian Coast Guard assets and US Coast Guard surface assets into the area over the course of the next couple of days.”

The US Coast Guard also has been in touch with the US Navy and the Canadian military to determine what underwater rescue capability is available, if needed, Mauger said.

OceanGate is assisting in the search and said it is “exploring and mobilizing all options to bring the crew back safely.”

“Our entire focus is on the crewmembers in the submersible and their families. We are 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 group said. “We are working toward the safe return of the crewmembers.”

Chief Mi’sel Joe of Miawpukek First Nation, which co-owns the Polar Prince, the support vessel on the expedition, said he received a call Sunday afternoon alerting him the sub was two hours overdue and still hadn’t surfaced, and they had lost communication with the sub. At that point, requests for search and rescue had gone out, he said.

The US Coast Guard tweeted Monday night that its C-130’s had returned to North Carolina and the P-8’s would resume their searches in the morning.

The Polar Prince and the Air National Guard’s 106th Rescue Wing would continue surface searches through the evening, according to the Coast Guard.

Sub has safety features, company says

OceanGate Expeditions operates a trip taking passengers to the Titanic’s wreckage at the bottom of the ocean for prices starting at $250,000, according to an archived version of its website, accessible via the Internet Archive’s Wayback Machine.

“Follow in Jacques Cousteau’s footsteps and become an underwater explorer — beginning with a dive to the wreck of the RMS Titanic. This is your chance to step outside of everyday life and discover something truly extraordinary,” the website said. “Become one of the few to see the Titanic with your own eyes.”

The eight-day expedition is based out of St. John’s, Newfoundland and begins with a 400-nautical-mile journey to the wreck site. There, up to five people, including a pilot, a “content expert” and three paying passengers, board a submersible named “Titan” and descend over two hours to the bottom of the ocean to see the Titanic up close.

According to OceanGate, Titan is a 23,000-pound submersible made of carbon fiber and titanium. As a safety feature, the sub uses a “proprietary real-time hull health monitoring (RTM) system” that analyzes the pressure on the vessel and the integrity of the structure, the company states.

The Titanic infamously hit an iceberg on its maiden voyage and sank in the North Atlantic Ocean in April 1912, killing more than 1,500 people. The wreckage of the Titanic, discovered in 1985, sits in two parts at the bottom of the ocean nearly 13,000 feet below the surface, southeast of Newfoundland.

Unlike a submarine, a submersible has limited power reserves so it needs a mother ship that can launch and recover it, according to NOAA.

‘Think positive’ expedition participant on Polar Prince posts

An expedition participant on board the Polar Prince, the ship that launched the now-missing sub, said they are all “focused on board here for our friends.”

“We have a situation that is now the part of a major Search and Rescue effort, being undertaken by major agencies,” Rory Golden wrote on Facebook after being contacted by CNN. “That is where our focus is right now.”

He asked people not to ask for or speculate on the names of those on the missing sub.

“I have seen some comments already on social media that are highly inappropriate and insensitive,” he said. He added their online and internet options were being restricted “to keep bandwidth available for the coordinated effort that is taking place.”

“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,” he said. He ended the post thanking everyone and saying, “… think positive. We are.”

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