The implosion likely occurred near the Titanic shipwreck, where the submersible was headed.
"The debris is consistent with the catastrophic loss of the pressure chamber," Rear Admiral John Mauger, of the First Coast Guard District, told reporters.
"Our most heartfelt condolences go out to the loved ones of the crew."
An unmanned deep-sea robot deployed from a Canadian ship discovered the wreckage of the Titan on Thursday morning about 488 metres from the bow of the century-old wreck, 4 kilometres below the surface.
