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

The US Coast Guard say five people were on board when the submersible went missing, and a search operation is underway.

Here is what we know so far:

Where and when did the submersible go missing?

The submersible went missing on Sunday in the Atlantic, some 435 miles (700km) south of Newfoundland, Canada.

The Titan was launched as part of an expedition involving The Polar Prince, an icebreaker that was hired by OceanGate and formerly operated by the Canadian Coast Guard.

The ship ferried dozens of people and the submersible craft to the North Atlantic wreck site, where the Titan was scheduled to make multiple dives.

The Polar Prince is being used to search the surface where the submersible was launched.

It is understood from OceanGate that Titan has a 96-hour oxygen supply in case of emergencies meaning only around two days of "life support" remain.

The US Coast Guard Northeast said The Polar Prince and the 106th Rescue Wing would continue surface searches throughout Monday evening.

US Coast Guard Rear Admiral John Mauger said the "remote" location made the search operation a "challenge".

"We are deploying all available assets to make sure that we can locate the craft and rescue the people on board," he said.

What is the Titan?

The Titan is a small submersible operated by OceanGate - a US-based company which offers crewed submersibles for industry, research and exploration.

Tickets cost $250,000 (£195,000) for an eight-day trip including dives to the wreck.

According to the company, the Titan is capable of diving 13,120ft "with a comfortable safety margin".

It takes the craft around two hours to descend approximately 12,500ft - where the Titanic wreck lies in a trench in the Atlantic.

The vessel, which weighs around 23,000lbs (10,432kg), operates by pinging back a message every 15 minutes to signal to those ashore that it is safe.

However, Sky News understands that those pings have stopped.

In a May 2021 court filing, OceanGate said the Titan had an "unparalleled safety feature" that assesses the integrity of the hull throughout every dive.

At the time of the filing, Titan had undergone more than 50 test dives, including to the equivalent depth of the Titanic, the company said.

During its 2022 expedition, OceanGate reported that the submersible had a battery issue on its first dive and had to be manually attached to its lifting platform, according to a November court filing.

What do we know about the three passengers so far?

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".

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.

Read more:
Titanic submersible rescue operation a race against time
UK billionaire Hamish Harding on board missing Titanic submersible

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.

Pakistani businessman Shahzada Dawood and his son, Suleman, were also on board, their family said in a statement.

"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," the statement said.