A massive search and rescue effort is continuing in the North Atlantic after a submersible exploring the wreck of the Titanic went missing deep under the ocean on Sunday.
There are five people on board.
Researchers aboard the Polar Prince - its mothership on the surface - lost contact with the crew shortly after the Titan began its dive.
There is limited oxygen on board, and it is estimated that supplies are set to run out by around 10:00 GMT (06:00 EDT) on Thursday.
Undersea noises have now been detected in the search area, but it is not known where they are coming from or what they mean.
US, Canadian and French agencies are working together to locate the submersible, and the tour firm OceanGate says it is exploring all options to get it back safety. Here is what we know so far.
What's the latest on the search? A Canadian search plane picked up underwater noises on Tuesday and Wednesday.
Deep-sea experts say it is hard to determine what these noises might be without seeing the data.
But it is possible they could be short, sharp, relatively high frequency noises - made from within the vessel by hitting a hard object against the end of the sub.
The US Coast Guard says it does not know what the noises are at this point. It says the US navy is analysing the data, but so far it remains inconclusive.
The US Coast Guard has sent ROVs - remotely operated vehicles - to search under the surface in the area where sounds have been detected.
But so far, they have yielded negative results, it said.