Large banging noises had last night been detected in the search area, the US Coast Guard confirmed, but added that its initial attempts using underwater equipment had ‘yielded negative results’.
Nevertheless it sparked fresh hopes that the passengers onboard were alive and could be hitting te side of the craft with cups in a frantic attempt to be detected on sonar.
But at 12,500ft – nearly two-and-a-half miles – below the surface, there are possibly just two vessels on Earth capable of rescuing them.
In a heartbreaking plea today, one of Mr Harding’s close friends Jannicke Mikkelsen warned ‘we are losing time’.
The friend told BBC Radio 4’s Today programme this morning: ‘I’m nervous. I’m sick to my stomach with nerves. I’m terrified, I’m anxious. I’m not sleeping at the moment. I’m just hoping for good news. Every single second, every single minute feels like hours.’
Colonel Terry Virts, another friend who dubbed Mr Harding ‘the quintessential British explorer’, also stressed that ‘the clock is ticking’ to find the five onboard.
Meanwhile retired British navy rear admiral Chris Parry’ told LBC that hopes of finding the missing deep-sea vessel without an ’emitting signal’ will be ‘impossible’ to find in the timescale.