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A search for a British TV doctor who vanished in the Greek Islands will now focus on a maze of tunnels known as 'The Abyss'.
Dr Michael Mosley was last seen on Wednesday after he left friends to go on a coastal walk along Saint Nicholas Beach on the Greek Island of Symi.
At least 100 rescuers and volunteers, including a helicopter, have been scouring the area between Agios Nikolaos and the island's main town in search of the 67-year-old.
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Firefighters are now probing an area dubbed The Abyss, a water-filled cave tunnel system believed to be kilometres long.
Greek authorities believe that Mosley may have been on a walk at the time, with the local Mayor commenting that it was an unusual route to have taken.
In a statement yesterday, Mosley's wife Clare said the days in which her husband went missing were "the longest and most unbearable".
"The search is ongoing and our family are so incredibly grateful to the people of Symi, the Greek authorities and the British Consulate who are working tirelessly to help find Michael," she said.
The couple's four children are on their way to the island to aid in the search.
Mosley is well-known in Britain for his regular appearances on television and radio and for his column in the Daily Mail newspaper.
He is known outside the UK for his 2013 book The Fast Diet, which he co-authored with journalist Mimi Spencer.
The "5:2 diet" set out how people can lose weight fast by minimising their calorie intake for two days a week while eating healthily on the other five.
He has subsequently introduced the Fast 800 diet, a rapid weight loss program, and has made a number of films about diet and exercise.
Mosley has often pushed his body to extreme lengths to see the effects of his diets and also lived with tapeworms in his guts for six weeks for the BBC documentary Infested! Living With Parasites.
