Friends, well-wishers and colleagues of Shahzada Dawood have sent messages of support and hope for the British-Pakistani billionaire who went missing in the Atlantic Ocean aboard a tourist submersible on a mission to view the wreckage of the iconic ocean liner the Titanic.

Engro Corp Vice Chairman Dawood, 48, who was accompanied by his 19-year-old son Suleman, was among five people, including UAE-based British billionaire explorer Hamish Harding who collaborated with the Indian government to reintroduce eight wild cheetahs from Namibia to India, who went missing near the wreck of the Titanic.

The 2-feet vessel was taking the group on an eight-hour trip to the bottom of the Atlantic to see the Titanic shipwreck on Sunday morning.

On Tuesday, search parties raced against time to find the deep-diving submersible which as of Tuesday night had an estimated 40 hours of oxygen left, the Dawn newspaper reported.

In a statement to the media, Dawood’s family described him as being a photography enthusiast. His 19-year-old university student son was a big fan of science fiction literature.

Social media was flooded with messages and prayers from friends, well-wishers and colleagues of Dawood for the two missing British-Pakistanis, who live in Surrey and had flown to Canada for the voyage.

His wife, Christine, and their daughter were on the mothership at the time of the submarine’s descent and await their safe return, the report said. The Titanic site is about 1,450 km east of Cape Cod and 644 km south of St. John’s, Newfoundland.

Engro Corp put out a statement summarising the events surrounding the expedition, saying, “We at Engro remain in prayer for their swift and safe return.” British billionaire Hamish Harding, French explorer Paul-Henri Nargeolet, and OceanGateCEO Stockton Rush are the other passengers on board the craft.

US and Canadian aircraft have searched about 7,600 square miles, larger than the state of Connecticut, Captain Jamie Frederick told reporters at a press conference on Tuesday.

The search, initially restricted to the ocean’s surface, was expanded underwater on Tuesday.

The US Coast Guard said they had commenced a remotely operated vehicle dive at the last known location of the sub, the report said.

The wreck of the Titanic, the infamous ship that sank in April 1912, lies around 700km south of St. John’s, Newfoundland, in Canada. The rescue mission for the missing sub is being run from Boston in Massachusetts and the US Coast Guard has said a research ship called the ‘Polar Prince’ had conducted a surface search for the sub on Monday evening.

It is used to transport submersibles to the wreckage site and was the support ship on Sunday’s tourist expedition.