France will send a ship equipped with a deep-sea diving vessel to help the search-and-rescue operation for a disappeared submersible that took wealthy tourists to visit the site of the Titanic wreckage, the French government says.
The ship, called the Atalante, is managed by the Ifremer research institute.
Ifremer said it had been contacted on Monday by the US navy with a request for help.
"It carries the Victor 6000 autonomous robot, capable of descending to a depth of 6000 metres, beyond the 3800 metres of the wreck's position," Ifremer said, adding the ship was expected to arrive on the site by Wednesday evening local time.
Additional crew members from another ship are also being urgently dispatched to the search operation.
Those aboard the submersible called Titan, the highlight of a tourist expedition that costs $US250,000 ($A367,000) per person, included British billionaire Hamish Harding and Pakistani businessman Shahzada Dawood with his son Suleman.
A government source confirmed to Reuters that a French citizen, the 77-year-old French explorer Paul-Henri Nargeolet, was among those on board the missing vessel.
