The hunt for the missing Titan submersible is still an active search and rescue mission, according to the head of the operation.

Rear Admiral John Mauger said conditions for the search are favourable and rescue teams are keeping the five crew members and their families in their thoughts as they continue the search.

His comments come despite the US Coast Guard estimates that the air supply in the vessel would run out at 12:08pm Irish time on Thursday.

“We continue to keep the crew members and families in our thoughts,” said Rear Admiral Mauger.

He said the mission was “still an active search and rescue right now”, adding that, "Conditions for the search and rescue are favourable right now.”

Meanwhile, a French research vessel carrying a deep-sea robot called Victor 6000 has now joined the search.

It has remotely controlled arms that can cut cables and perform other manoeuvres to release a stuck vessel - and its 6,000m diving capability means it can go even deeper than the Titanic itself.

The vessel - operated by the US-based firm OceanGate - had five men on board when it went missing.

They are, British billionaire Hamish Harding, British businessman Shahzada Dawood, his son Suleman Dawood, OceanGate's US-based chief executive and founder Stockton Rush and French submersible pilot Paul-Henri Nargeolet.

The search area now covers an area roughly the size of the US State of Connecticut and involves camera equipment scanning the sea floor.

Safety concerns were raised about the Titan in 2018; the Marine Technology Society said it had “concern regarding the development of Titan and the planned Titanic Expeditions” and warned against the “current experimental approach adopted by OceanGate”.

With reporting from Micheal Staines and IRN.