Contact with the small sub was lost about an hour and 45 minutes into its dive, the US Coast Guard said.

Tour firm OceanGate said all options were being explored to rescue the five people onboard.

Tickets cost $250,000 (£195,000) for an eight-day trip including dives to the wreck at a depth of 3,800m (12,500ft)

In an update on Tuesday, Captain Jamie Frederick said the search for the vessel, called Titan, had not yielded any results so far.

An ROV (remotely operated underwater vehicle) has been deployed at the site and has a camera on board.

A unified command has been set up, consisting of "expertise from the United States Coast Guard, the United States Navy, Canadian Armed Forces and Coast Guard, and the Titan's parent company, Ocean Gate Expeditions", Mr Frederick said.