Loved ones of the five people onboard the missing Titanic submersible have asked people to pray for their safe return home.
The submarine-like vessel is trapped beneath the Atlantic Ocean with three British passengers on board, including Pakistani British-based businessman Shahzada Dawood and his 19-year-old son, Sulaiman Dawood.
British billionaire adventurer Hamish Harding is also on the vessel, as is French submersible pilot Paul-Henry Nargeolet, and chief executive and founder of OceanGate Expeditions, Stockton Rush.
The 21ft vessel was taking the group on an eight-hour trip to the bottom of the Atlantic to see the Titanic shipwreck on Sunday morning - with tickets costing close to £200k, the Mirror reports.
But rescuers fear they may not reach the vessel in time before its oxygen supply cuts out after it lost contact around one hour and 45 minutes after it submerged.
The Dawood and Harding families have asked for privacy but say they are grateful for the messages of support and concern they have received.
Naval teams from across US, Canada and the UK are desperately trying to locate the vessel and rescue passengers before the oxygen supply cuts out in around 50 hours.
One explorer and friend of missing British billionaire Hamish told Sky News she is "terrified" that the five could be at the bottom of the ocean running out of air.
"This is what I fear the most," Jannicke Mikkelsen said.
Shahzada and son Sulaiman belong to one of Pakistan's most prominent families and are both British citizens. Their family say they are "praying to Allah" for their safe return.
In a statement, they said: “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."
Private plane firm Action Aviation said the family of its missing chairman Hamish Harding are "very grateful" for the "kind messages” and they have chosen to express optimism over a rescue, saying they "look forward to welcoming him home."
The first British diver to see the wreck of the Titanic said that Paul-Henry is an “extraordinary explorer and an incredible individual”.
Dik Barton, who made 22 dives to the wreck, said the group had “good leadership” in pilot Paul-Henry as "he knows the wreck better than anybody."
Dik continued: "He is the kind of man who will keep them calm, but it’s not easy in a tube at the bottom of the ocean."
David Mearns also knows Paul Henry professionally and is personal friends with Hamish.
Mr Mearns said: "When I found out initially that Hamish was on board that was very upsetting and then when later in the day that PH was also with him on the sub, which was almost a typical thing to expect, they would have got on fantastically well these two characters, that really started to make the day a lot worse."
Oceanologist Dr Simon Boxall, of the University of Southampton, said a distress signal was sent out by the submarine.
Dr Boxall said: "This is second-hand knowledge but my understanding is that they have received a signal from the submarine.
"You can't use radios underwater. You rely totally on 'pings'. What they have is really limited communication.
"Apparently they have had, and I don't know when ... they have had an emergency ping saying the vessel is in distress.
“I don't know if that is automatically generated or generated by people on board.
"It could be that the vessel is lost already or it could be automatic."
The Foreign Office says it is aiding the families of three British nationals on the missing Titan submersible.
The Titanic's wreck lies 435 miles south of St John's Newfoundland, with the recuse mission being run from Boston, Massachusetts.
At a press conference about the missing submarine, Rear Adm. John Mauger confirmed that was designed with 96 hour emergency oxygen capability
"We anticipate there is somewhere between 70 and the full 96 hours available at this point," Mauger says.
Speaking from where the rescue operation was being led in Boston, Rear Admiral John Mauger, said “everything was being done” to find the submersible.
He said it included specialised submarine detection planes, the US Coastguard, the Canadian military, and commercial ships.
Sonar buoys that can listen to a depth of 13,000ft have been placed in the water.
The Titanic lies at 12,500ft on the ocean bed.
In a short statement released today, a spokesperson said: "We are in contact with the families of three British nationals following a submersible going missing off the coast of North America and are in touch with the local authorities."
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