The five people on board the missing submersible close to the wreck of the Titanic have “about 40 hours of breathable air” left, the US Coastguard has said.
In an update on Tuesday, Captain Jamie Frederick said the search had not yielded any results so far.
An ROV (remotely operated underwater vehicle) has been deployed at the site and has a camera on board.
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A unified command has been set up, consisting of “expertise from the United States Coast Guard, the United States Navy, Canadian Armed Forces and Coast Guard, and the Titan’s parent company, Ocean Gate Expeditions”, Mr Frederick said.
Since Sunday, combined search efforts have covered an area of 7,600 square miles, he added.
A Canadian P-3 aircraft is conducting a six hour search of the area and several C-130 aircraft and another P-3 are scheduled to fly on Tuesday afternoon and evening, he said.
The combination of a surface search and a subsurface search make it an “incredibly complex operation”, Mr Frederick said.
The Coast Guard and other search and rescue crews have swarmed a remote area in the Atlantic in search of the vessel, called Titan, which went missing on Sunday with five people on board.
Rescuers have expanded their search into deeper waters.
It is understood from the vessel’s operator, OceanGate Expeditions, that Titan had a 96-hour oxygen supply in case of emergencies.
The five people on board are British billionaire Hamish Harding, Pakistani businessman Shahzada Dawood and his son Suleman, chief executive and founder of OceanGate Expeditions Stockton Rush, and French submersible pilot Paul-Henri Nargeolet.
Mr Dawood is married and has two children, the family said in a statement. He is vice chairman of Pakistan’s Engro Corporation.
He and his son Suleman, who is currently studying at university, are British citizens.
The major search and rescue operation is taking place some 435 miles south of Newfoundland, Canada, involving the US Coast Guard as well as Canadian and US aircraft.
The Canadian research icebreaker Polar Prince, which was supporting the Titan, reportedly lost contact with the vessel about an hour and 45 minutes after it submerged.
The wreckage of the Titanic that sank in 1912 after hitting an iceberg lies at about 12,500 feet (3,810 metres).
The Titan submersible usually takes two hours to descend to the wreck.