One of Pakistan's richest men and his teenage son are among the five people missing in the submarine that set off to see the wreck of the Titanic before losing all communication thousands of feet underwater in Atlantic Ocean. 

Shahzada Dawood, 48, a UK-based board member of the Prince's Trust charity, and his son Sulaiman Dawood, 19, were on board the tiny underwater craft taking paying tourists to view the famous wreck 12,500ft underwater when they lost signal in the dark depths of the Atlantic Ocean, 370 miles off the coast of Newfoundland, Canada.

Their desperate family, including Shahzada's wife Christina and daughter Alina, are now enduring an agonizing wait for any news of the pair - hoping in vain that they could somehow be found thousands of feet underwater before the oxygen onboard runs out in around 50 hours. 

'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 Dawood family said in a statement.

The Dawood family are among the richest in Pakistan, but have strong links to the UK and Shahzada is believed to live in a Surrey mansion with Christine, who works as a life coach, son Sulaiman and daughter Alina.

Shahzada is the Vice Chairman of Engro Corporation, which makes fertilisers, food and energy, as well as the Dawood Hercules Corporation, which makes chemicals. He was born in Pakistan but moved to the UK where he studied law at the University of Buckingham. 

The missing tourist submersible with five people aboard including British billionaire Hamish Harding is understood to have last 'pinged' while it was directly above its destination - the Titanic. Paul-Henri Nargeolet, the French world-renowned explorer, is also onboard. OceanGate CEO Stockton Rush is believed to be the fifth crew member.

There is now a desperate race against time for rescue crews from the US and Canada to find the 21ft vessel, which is understood to have last 'pinged' whilst it was directly above the Titanic wreck, before the air onboard runs out. It is believed the submarine has enough oxygen to last underwater until 12pm on Thursday UK time (7am EST).

If the submersible is intact, the five people onboard will be facing dwindling oxygen levels and fighting the cold and facing the risk of hypothermia, David Gallo, senior advisor for Strategic Initiatives, RMS Titanic, which owns the salvage rights to the Titanic wreck site, told CNN.

He said hypothermia will be a risk 'if the sub is still at the bottom, because in the deep ocean it is just above freezing cold'. 'One of the biggest things is where is it? Is it on the bottom, is it floating, is it mid-water? That is something that has not been determined yet... We will have to wait and see and hope for the best,' Gallo added.

The sub, owned and operated by OceanGate Expeditions, had launched at around 4am on Sunday and was taking the crew of five 12,500ft underwater as part of its £195,000-a-head tour of the 1912 shipwreck of the Titanic. 

But the crew lost communication with the sub's mothership MV Polar Prince an hour and 45 minutes into the two-hour descent and there is now a desperate search to find the vessel and those on board before the air runs out. 

And as the terrifying race against time began yesterday afternoon, rescuers admitted the sub could have become stuck in the wreckage of the Titanic which is 370 miles from Newfoundland in Canada but lies in US waters.

Submarine experts also fear the vessel is too deep for a manned rescue sub, such as the US Navy sub which is limited to 2,000ft, and that the only way of reaching it may be using a remote operated vehicle. These can reach a maximum depth of 20,000ft.

Gallo said that if the submersible is located, the rescue crew would find it difficult to rescue those on board the vessel. 'The water is very deep - two miles plus. It's like a visit to another planet, it's not what people think it is. It is a sunless, cold environment and high pressure,' he said.  

The desperate families of those on board - Shahzada Dawood and his son Sulaiman, Mr Harding, Mr Nargeolet and Mr Rush - are now desperately waiting for news of their loved ones.

The Dawoods are members of one of the most prominent business families in Pakistan. Shahzada's father Hussain, 79, is the Chairman of the Dawood Hercules Corporation, which makes chemicals, and the Engro Corporation, which makes fertilisers, food and energy. 

Shahzada is vice chairman of both companies and is also a member of the Global Advisory Board for King Charles' Charity, Prince's Trust. He is also in the Founder's Circle of the British Asian Trust. 

The father-of-two is also on the board of trustees for the California-based SETI Institute that searches for extraterrestrial intelligence. 

Shahzada was born in Pakistan but moved to the UK to study law at the University of Buckingham. He then went on to study at Master's in textile marketing in 2000 at Philadelphia University.

Shahzada had decided to take his son Sulaiman on the 'Titan' - the name of the Titanic submersible - for the five-day trip with three others when disaster struck and they lost contact with the surface after appearing to close in on their destination.

It's understood that Titan communicates by sending a ping to the Polar Prince every 15 minutes - the last of which was received while the submersible floated above the Titanic wreckage at about 10am EST yesterday (3pm UK time).

It was at that moment that chaos ensued. A distress call was sent to the US Coast Guard at 9pm, whose Boston branch is leading an operation to carry out what would be the deepest undersea rescue mission ever.