It is not clear how many people, if any, were on board at the time, and it is understood that coastguards are looking for the vessel in the North Atlantic Ocean.

The Ministry of Defence has said it is continuing to "monitor the incident".

Sky News has located the Polar Prince tugboat that is on the water around 700m away from the Titanic wreck site, via the website MarineTraffic.

The tugboat is used to transport submersibles.

The main difference between a submersible and a submarine, is that the former needs a mother ship that can launch it and recover it, while a submarine has enough power to leave port and come back to port under its own power.

In a statement, a spokesperson for the Ministry of Defence said: "As the host nation for NATO's multinational submarine rescue capability, we continue to monitor the incident in the North Atlantic and will guide and assist in any response activity as appropriate."

Tourists sometimes pay tens of thousands of dollars to be taken to the wreckage of the liner - 12,500ft under water.

OceanGate Expeditions is a company that deploys submersibles for deep sea expeditions - including to the wreck of the Titanic. The company has not commented on the reports.

The Titanic sank into the Atlantic on 15 April 1912 during its maiden voyage from Southampton to New York after hitting an iceberg, with some 1,500 people dying in the disaster.

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The wreck - discovered 37 years ago - is in the Atlantic about 400 nautical miles from Newfoundland in Canada.

Last month, the first-ever full-sized digital replica of the Titanic was created as experts said it could be used to unlock secrets of the world's most famous shipwreck.