Rescue teams have entered “The Abyss” in a desperate search for TV doctor Michael Mosley.
Police and firefighters have ramped up their hunt to locate the missing medic and have entered a complex series of underground tunnels.
The British doctor, 67, vanished during a walk on the Greek island of Symi on Wednesday.
The presenter is said to have left St Nicholas Beach in Symi solo on Wednesday at 1:30 pm to return to where he, his wife Dr Clare Bailey, and their two friends were staying in Pedi.
A rescue operation to find him has now entered its fourth day and fire crews are scouring inside the group of water-filled tunnels near Agia Marina.
The bottomless network of tunnels is said to spread for many kilometres.
A waiter who works close by said: “It’s like a deep system of tunnels, but it is full of water and can spread for kilometres.
“If there is a hole and you fall, you lose your sense of balance and drown there.
“There is a reason they call it ‘The Abyss’. There is something very strange going on,” reports The Telegraph.
CCTV appeared to show Mosley walking with an umbrella near to the marina in the village of Pedi in Symi.
And previous footage from a house at the edge of Pedi’s small marina showed the presenter walking towards a mountainous path at about 2pm local time on Wednesday.
The mayor of Symi, Eleftherios Papakaloudoukas, questioned how anyone could survive in the heat that topped 40C on the day Mosley disappeared.
The hot and dry conditions making search efforts much more challenging.
One uniformed worker told OK! 10 rescuers were making their way across multiple summits in the search for the health and diet guru.
Firefighter Stergos Giakoumakis told the publication: “It’s not so easy to bring here 100 people, especially this period because it’s the most dangerous period.
“Everything is dry and it is too dangerous for firemen to search.”
Dr Mosley’s wife Clare and his four children have also been looking for him near the town of Pedi as he was last seen heading towards a mountain trail known as Agia Marina.