Missing Titanic tourist sub passengers have just 40 hours of breathable air left

He said: "We know from the data that we were using as a starting point was 96 hours.

"We know at this point, we’re approximately about 40, 41 hours."

Captain Frederick reiterated that the estimate of 40 hours is based on the initial report of 96 hours.

The announcement means passengers have until around 10am (BST) on Thursday.

Efforts to recover the five-person submarine "have not yielded any results".

The Titan vessel vanished while conducting a Titanic tourist venture in the depths of the Atlantic Ocean.

Titanic's wreck sits about 3,800m (12,500ft) below sea level at the bottom of the ocean around 370 miles off the coast of Newfoundland but in US waters.

British billionaire Hamish Harding, 58, is among those missing as rescue crews continue to search the Atlantic Ocean.

Harding's stepson Brian Szasz confirmed he was missing on social media yesterday.

He wrote on Facebook: "Thoughts and prayers for my Mom and Hamish Harding."

The stepson added: "Hamish Harding my stepfather has gone missing on submarine thoughts and prayers."

Shehzada Dawood and his son Suleman from Pakistan were onboard the five-person expedition.

French diving expert Paul-Henry Nargeolet and submarine boss Stockton Rush are also thought to be on the missing submarine.

It costs around £200,000-a-head to embark on the tourist voyage.