A submersible used to visit the wreck of the Titanic has gone missing just weeks after the US and UK called for greater protection for the site.

A US Coast Guard operation is underway after a company that runs tours to the ship said that it had lost contact with the small carbon fibre vessel, according to reports.

It was not clear how many people were on board the submersible, reportedly operated by OceanGate Expeditions, a private company which runs eight-day trips to the area.