Rescuers are racing against the clock to find a British billionaire and four other people missing in a deep-sea vessel near the wreck of the Titanic ocean liner before their breathable air runs out. The US Coast Guard is leading the search for the small craft, named Titan, which was reported overdue about 435 miles (700km) south of St John's in Newfoundland, Canada, on Sunday.
Titan's dive was one of many that have been made to the wreck, which is about 2.4 miles (3.9km) below the surface, by OceanGate Expeditions since 2021. With the temperature on the ocean floor near freezing and an estimated 40-hour oxygen supply remaining on the vessel, the occupants are at increasing risk of hypothermia or suffocation.
Here the PA news agency sums up what we know so far:
What has the US Coast Guard said?
The US Coast Guard announced on Wednesday morning that "underwater noises" have been detected in the search area.
It tweeted: "Canadian P-3 aircraft detected underwater noises in the search area. As a result, ROV (remote operating vehicles) operations were relocated in an attempt to explore the origin of the noises. Those ROV searches have yielded negative results but continue.
"Additionally, the data from the P-3 aircraft has been shared with our US Navy experts for further analysis which will be considered in future search plans."
The P-3 submarine hunter is described by its manufacturer, Lockheed Martin, as "the ultimate maritime patrol aircraft" and was used in the Cuban Missile Crisis, Hurricane Katrina and the BP Horizon oil rig disaster in the US. On Tuesday, Captain Jamie Frederick, of the US Coast Guard, said a "unified command" of multiple agencies has been formed to tackle the "very complex problem" of finding Titan.
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He told a press conference in Boston there were "approximately 40/41 hours" of breathable air, out of the vessel's reported 96-hour oxygen supply, left on board.
He added: "Since Sunday, the Coast Guard has co-ordinated search efforts with the US and Canadian Coast Guard, Air National Guard aircraft and the Polar Prince, which has searched a combined 7,600 square miles, an area larger than the state of Connecticut."
He said these efforts have involved aircraft searching by sight and with radar and sonar buoys, and that on Tuesday Deep Energy, a 637ft (194m) pipe-laying vessel with "underwater ROV (remotely operated vehicle) capability", had joined the search. Capt Frederick said several private research vessels with "ROV capabilities are making preparations to join the efforts".
But he was non-committal when asked if there is any way to retrieve the submersible and save the five people on board if it can be located, saying experts will look at the next course of action if they get to that point.
Who is in the vessel?
British billionaire Hamish Harding and four other passengers are on board the 22ft (6.7m) long OceanGate Expeditions vessel. They are UK-based businessman Shahzada Dawood and his son Suleman, reportedly together with French submersible pilot Paul-Henri Nargeolet.
On Tuesday, OceanGate confirmed that its chief executive and founder, Stockton Rush, "is aboard the submersible as a member of the crew". On social media at the weekend, Mr Harding said he was "proud to finally announce" that he would be joining the mission to the wreck of the Titanic.
Mr Harding holds three Guinness World Records - for longest duration and distance traversed at full ocean depth by a crewed vessel, and fastest circumnavigation via both poles by aeroplane. In June 2022 he went into space on Blue Origin's New Shepard rocket.
His cousin, Kathleen Cosnett, told the Daily Telegraph she sees him as "daring" and "inquisitive", and that she was "devastated" to learn he was missing. A family statement obtained by CNN on Tuesday confirmed Mr Dawood and his son, who belong to one of Pakistan's most prominent families, are on board.
Mr Dawood is the vice chairman of Pakistani conglomerate Engro Corporation, which was founded as a fertiliser business, and is a long-time supporter of The Prince's Trust International and The British Asian Trust, both of which are charities founded by the King. It is understood that Charles has asked to be kept up to date with the situation and that his thoughts and prayers are with the Dawood family and all those involved.
The Dawood family, who live in Surbiton, south-west London, are in Canada for a month, the PA news agency understands. Mr Rush originally trained as a pilot, becoming the youngest jet transport-rated pilot in the world in 1981 at the age of 19, according to his profile on the OceanGate website. He has been married to Wendy Rush, nee Weil, since 1986, with their wedding announcement published in the New York Times.
In a 2017 interview with the alumni magazine for Princeton University, where he studied mechanical aerospace engineering, he said: "I was interested in exploration. I thought it was space exploration. I thought it was Star Trek and 2001: A Space Odyssey and Star Wars... and then I realised it's all in the ocean."
A former commander who served in the French navy for 25 years, Mr Nargeolet, reported to be 77, was in the first human expedition to visit the ship in 1987, according to the Telegraph. As director of the Underwater Research Programme with RMS Titanic Inc, he led the retrieval of items from the sunken liner across several expeditions. He lives in Connecticut, US, while his adult children live in Cork, Ireland, the Telegraph has reported.
What are conditions on board Titan like?
The submersible, a Cyclops-2 model, is the second Cyclops model built by OceanGate, after the Cyclops-1. There are no doors on the craft, so passengers begin their journey by climbing in through an entry hatch which is then bolted shut from the outside before they descend 13,000ft (2.4 miles) beneath the ocean surface to the Titanic, Mail Online reported.
There are no seats on the 22ft (6.7m) long, 9.5ft (2.9m) wide and 9.2ft (2.8m) high cylindrical vesssel, meaning passengers must sit on the hard floor without shoes, which they are required to leave behind. If they need the toilet, they must use a small black box separated by a curtain from the rest of the crew.
Cut off from communication with the outside world, they have no idea whether they will ever be found. There are no windows except a small porthole directly next to the toilet at the front of the craft, which is also the primary viewpoint to look out at the Titanic. When the craft was still operational, the pilot used a modified Logitech games controller to steer it.
What other dangers await the passengers?
Even if rescuers locate the craft before its oxygen supply runs out, the occupants face other dangers. One possibility is that they are stranded at the bottom of the ocean near the site of the Titanic, about 370 miles (595km) off the coast of Newfoundland, Canada.
If that is the case, those on board will be faced with a rapidly dropping temperature which puts them at risk of hypothermia. Rescuers are in a "race against time" to reach the vessel before the oxygen runs out, which is expected to happen on Thursday.
David Gallo, senior adviser for strategic initiatives for RMS Titanic, told CNN that temperatures on the ocean floor are "just above freezing cold".
He said: "It is a race against time - you are fighting oxygen levels, also fighting the cold if the sub is still at the bottom, because the deep ocean is just above freezing, so hypothermia is an issue. 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."
Could passengers suffer 'the bends'?
According to oceanologist Dr Simon Boxall, of the University of Southampton, one common misconception is that people will get decompression sickness, commonly known as "the bends", if the submersible moves up to the surface too quickly. He told PA that those on board would not suffer "ill-effects" because the vessel is at atmospheric pressure.
He also said it is a mistake to believe passengers could use escape hatches, because if they did they would be crushed. He told GB News that the craft is not above the surface because if this was the case crews would be able to use radios.
What is the latest on their condition?
Rescue operations are continuing after noises were detected from the search area. The Explorers' Club, of which Mr Harding is a founder member, shared an upbeat message on Wednesday morning that there is "cause for hope".
President Richard Garriot de Cayeux said they are ready to provide the UK-based Magellan's remotely operated vehicle (ROV) which is certified to travel as deep as 3.7 miles (6,000m). In a statement on its website, deep water specialist Magellan said it was contacted by OceanGate on Monday and "immediately" offered knowledge of the site and expertise in operating at depth.
The company added that it has been working with UK and US agencies to move its specialist equipment and support crew to St John's, Newfoundland, following instructions to mobilise from OceanGate. "Magellan is 100% focused on supporting the rescue mission to recover the submersible," the organisation said.
