The air supply on the Titanic tourist submarine has reportedly expired as rescuers continue their desperate search for the five missing passengers.

A US Coast Guard spokesperson said they expect the vessel, named Titan, will run out of oxygen at 1pm today, according to the Irish Times.

This estimated time is based on the number of hours of oxygen the craft had for the five people on board - 96 hours worth - and the time it submerged - 1pm UK time on Sunday, June 18th.

Other deadlines, such as 12:08pm today, have been reported but the US Coast Guard said they did not know where that time had been sourced from. "Based on the approximate 96 hours of oxygen supplies on the vessel at the time of deployment, any other estimates [than 1pm UK time on Thursday] would be too uncertain for us to confirm," they said.

A Canadian aircraft searching for the vessel deep in a remote part of the North Atlantic ocean detected intermittent "banging" noises from the vicinity of its last known location, the US Coast Guard said.

A photo showing the tiny space inside the Titan. Credit: Irish Times.

The frantic last-ditch search for the stricken Titanic tourist submersible has ramped up, with more ships joining the rescue effort as oxygen levels on board dwindled. It is hoped that the additional personnel will be enough to save the five crew members on the OceanGate Expeditions sub before oxygen runs out.

An Irish diver who is currently on board the ship that launched the missing submarine near the Titanic wreck has praised the "truly astonishing" rescue effort underway.

Rory Golden, owner Flagship Scuba in Dublin, has previously visited the Titanic site on two occasions. In May, he joined the OceanGate Expeditions vessel in Newfoundland before it travelled with the submarine and passengers towards the Titanic site.

In an update on his social media, Golden said, "The reaction and offers of help globally is truly astonishing, and only goes to show the real goodness in people at a time like this. Our online and internet options are being restricted in order to keep bandwidth available for the co-ordinated effort that is taking place, so please bear that in mind too."

Before his career in Flagship Scuba, Dublin, Golden was a manager in Virgin Records for fifteen years.

A second vessel has also detected noises in the area where rescuers are searching for the submersible. The full scope of the search was twice the size of Connecticut in waters 4km deep, said Captain Jamie Frederick of the First Coast Guard District.

"This is a search-and-rescue mission, 100pc,” Frederick said. “When you’re in the middle of a search-and-rescue case, you always have hope. We’ll continue to put every available asset that we have in an effort to find the Titan and the crew members."

Retired Navy captain Carl Hartsfield, now the director of the Woods Hole Oceanographic Systems Laboratory in Massachusetts, said the sounds had been described as "banging noises", but warned that search crews "have to put the whole picture together in context and they have to eliminate potential manmade sources other than the Titan"

Even those who expressed some optimism warned that many obstacles remain: from pinpointing the vessel’s location, to reaching it with rescue equipment, to bringing it to the surface – assuming it’s still intact – before the passengers’ oxygen supply runs out.