Watch: The latest on the Titanic sub... in 70 seconds
The search for the about the Titan submersible has been expanded to include aircraft and ships, as well as remotely operated vehicles, combing around 10,000 sq miles of ocean.
Noises have been heard in the search but it remains unclear what they are, and the US Coast Guard says this remains a search and rescue operation.
Contact with the sub - which has five people on board - was lost on Sunday as it made a descent to the Titanic wreck.
The BBC's Jon Amos looks at what we know so far about the lost sub.
Video by Mattea Bubalo