And, Reuters is learning more about the people aboard the vessel, which authorities say can only operate for about 96 hours underwater.

Contact was lost on Sunday, and it's not clear what condition the vessel is in.

So who is aboard?

One of the missing persons is reportedly Stockton Rush, the founder of a company called OceanGate, which ran the operation.

Reuters met Rush in 2017, where he talked about the company. This is what he said at the time:

"There are five individuals that can go on each dive. Three of those are what we call mission specialists. So those are the folks who helped finance the mission, but they are also active participants. So why we are not a fan of the 'tourist' term is because these are crew members. We teach them how to operate the sonar, how to operate the communications systems..."

"You're part of the crew."

Hamish Harding, a British billionaire, is believed to be aboard and said on social media that he was one of the "mission specialists."

He lives in Dubai and is the chairman of an aviation consultancy. He's an adventurer. He once accompanied Buzz Aldrin, the former astronaut, on a trip to the South Pole when Aldrin became the oldest person ever to reach Antarctic.

Four years ago he was also aboard an aircraft that set a world record for fastest circumnavigation of the Earth over the north and south pole.

Harding is accompanied on the Titanic trip by Shahzada Dawood and Dawood's son, Suleman. Dawood is an executive at one of Pakistan's largest conglomerates, Engro Corporation, and lives in the UK.

But he's also a trustee at the famed SETI Institute, also known as the Search for Extraterrestrial Intelligence in California. Their website says he's a philanthropist, loves animals, and has a wife and daughter as well.

The vessel is reportedly piloted by Paul-Henri Nargeolet, a French explorer and the director of underwater research at a company that owns the wreck of the Titanic. He's a former commander in the French Navy, and served as both a diver and mine sweeper.

He was on the first recovery expedition to the Titanic in 1987.