A submarine used to take tourists down to view the wreck of the Titanic has gone missing in the Atlantic Ocean, sparking a search and rescue mission.
OceanGate, the company operating the submersible, says it is "exploring and mobilising all options" to bring the crew back safely.
It is not clear how many people were on board at the time it went missing.
The submersible is an experimental sub, and crews embarking on an expedition are told of the dangers - like this warning given by the Oceangate chief executive to a crew last year.
Parks Stephenson, who advised director James Cameron for the film Titanic and has been to the wreckage, explains more about the submersible.
Our New York correspondent William Denselow is following developments and spoke with Corin Dann.