There is now just under 20 hours of oxygen left in the missing Titan submersible.
Sonar technology has since yesterday detected knocking sounds every half hour in the search area near the wreckage of the Titanic.
The US Coastguard says they are working closely with experts to locate the source of the sound but don't know what the noises are.
Corin Dann spoke to US correspondent, Caroline Maloney.
