A British rescue mission to locate a missing submarine has been "blocked by US officials" despite there being just hours until the five passengers onboard run out of oxygen.
A remotely operated vehicle capable of pulling the vessel - which takes tourists to the Titanic shipwreck - out of the Atlantic Ocean has been waiting to leave an airport in the Channel Islands since 7pm on Monday.
The team from deepwater specialists Magellan Limited has not received approval for take-off.
An urgent search off the coast of Newfoundland was launched after the submarine lost contact an hour and 45 minutes into its dive which began on Sunday morning.
The £200,000-a-head voyage takes tourists to the Titanic shipwreck which sits 3,800m (12,500ft) below sea level at the bottom of the ocean
Reuters
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.
The OceanGate sub's air supply is due to run out around 10am on Thursday UK time (5am EST).
It is understood that British billionaire Hamish Harding, 58, is among those missing as rescue crews search the Atlantic Ocean.
Harding, who runs an aviation company, was on the 21ft vessel when it set off on Sunday.
The father-of-two, who lives in the UAE, said he was “proud” to be joining OceanGate as a “mission specialist”, adding that the group included “a couple of legendary explorers”.
French diving expert Paul-Henry Nargeolet and submarine boss Stockton Rush are also thought to be on the missing submarine.
Shehzada Dawood and his son Suleman from Pakistan were also onboard the five-person expedition, according to a statement released by the family.
The final ping from a submarine before it vanished has revealed fresh details on the vessel's last known position.
The OceanGate Expeditions tour group, which takes explorers to the depths of the Atlantic for $200,000 per person, is believed to have lost contact when the vessel was directly above the Titanic wreck.
The submarine - named Titan - sends texts to communicate with their team on transport vessel the Polar Prince which remains above water.
Every 15 minutes, Titan sends "pings" to the Polar Prince and the final of these messages is thought to have been sent at around 3pm UK time on Monday.
Fears have been raised that Titan could be stuck in the wreckage of the Titanic which is too deep for rescuers to reach.
The Titanic tourist sub vanished in the Atlantic Ocean on Sunday, sparking an urgent search
ReutersSpeaking on GB News, Oceanographer Dr Simon Boxall said: "They're in a very difficult situation here, they're sitting in four kilometres, 13,000 feet of water. That's the limit of the subs capability anyway.
"They're in a very deep part of the ocean, they're a long way from the coast as well so getting any sort of rescue attempt to them is going to take time and there are very few vessels that are capable of going to those sorts of depths.
"The other problem is there's no easy communication method for that sort of depth. You cannot communicate with things like radios and things underwater. They're reliant on a series of sort of Sonic clicks and that's assuming that the receiver they have in the submarine is actually working."
He added: "And of course you know, we know obviously how long it took for us to discover Titanic and the size compared to the submersible significant gives you an idea of of how difficult this search is going to be."