OceanGate Expeditions, a company that deploys vessels for deep sea expeditions, confirmed that one of its submersibles had gone missing in the Atlantic Ocean after taking passengers to see the wreck of the Titanic.

A search remains ongoing.

Hamish Harding, 58, a UK billionaire was confirmed as one of the passengers, by his stepson Brian Szasz, who said on Facebook that his step father was in his "thoughts and prayers".

Sky News also understands that French submersible pilot, Paul-Henry Nargeolet, and chief executive and founder of OceanGate Expeditions, Stockton Rush, were also on board.

It is not clear how many people in total were on board, but the submersible has a capacity of five - a pilot and four guests.

What do we know about the three passengers so far?

Mr Harding is the current Chairman of Action Aviation - a sales and operations company that offers a range of services in the business aviation industry.

Posting on social media on Sunday, Mr Harding confirmed that he was joining OceanGate Expeditions - the company that supplied the vessel - as a mission specialist.

He wrote that due to bad weather in Newfoundland, Canada, the expedition was likely to be the first and only manned mission to the Titanic in 2023.

Based in the United Arab Emirates - where Action Aviation headquarters is - Mr Harding described himself on social media as a world explorer.

He holds the Guinness world record for the fastest circumnavigation of the Earth via the North and South Poles by an aircraft - 46 hours, 40 minutes and 22 seconds.

Last year he also took part in the fifth human space flight by Blue Origin - an American aerospace company founded by Jeff Bezos.

Stockton Rush is CEO and founder of OceanGate Inc - a company that provides crewed submersible services to enable researchers and explorers to access the oceans' vast resources.

Having trained as a pilot, he became the youngest jet transport rated pilot in the world at the age of 19.

He is also a founder and member of the board of trustees of non-profit organisation OceanGate Foundation, which aims to catalyse emerging marine technology to further discoveries in marine science, history, and archaeology.

In an interview with Sky News back in February, Mr Rush spoke about visiting the Titanic wreck.

"What really strikes you is how beautiful it is," he said. "You don't normally see that on a shipwreck.

"It is an amazingly beautiful wreck."

When asked if they can go inside the wreckage, Mr Rush said: "You can see inside, we dipped down and saw the grand staircase and saw some of the chandeliers still hanging.

"Next year we are hoping to send a small robot inside but for now we stay on the outside."

Paul-Henry Nargeolet is a former commander who served in the French Navy for 25 years.

During his service he became the captain of the deep submergence group of the navy.

After leaving the navy he joined the French Institute for Research and Exploitation of the Sea (IFREMER), according to The Five Deeps Expedition - a company that assembles scientists, engineers and submersible operators for missions.

Mr Nargeolet has already led several expeditions to the Titanic site and has been involved in numerous scientific and technical expeditions around the world.