TV Dr Michael Mosley has vanished 'without a trace' during a short 20-minute walk along the beach as he returned home on a Greek island.
The health expert is said to have forgotten his phone on Agios Nikolaos Beach in Symi, where he was shortly before disappearing on Wednesday.
A huge search and rescue operation was launched but so far no trace of him has been found.
Temperatures in the Dodecanese island Symi reached a scorching 37C today.
Police on the island fear the 67-year-old may "have fallen from a height" as he was walking the less-than-a-mile distance to Pedi where he was staying with his wife Dr Clare Bailey, 62.
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Dr Bailey alerted the authorities after her husband did not return home by 7.30pm.
Local authorities started retracing his steps to locate him while a search and rescue team from Athens with drones and other equipment joined their efforts.
A senior Greek official in charge of search and rescue operations in the Southern Aegean said "no stone" would be left unturned to find the Briton.
The security official told The Sun: "Since this morning we have had all available forces out there on the island and we have asked to bring in specially trained dogs and even a helicopter from Athens for back up too.
"No stone will be left unturned. Symi is a small island, he can’t just have disappeared."
Symi's mayor Lefteris Papakalodoukas told Proto Thema police and the fire brigade are working to locate the Brit.
He said: "The British broadcaster has come for holiday with his wife and is being hosted by a couple of their friends on our island.
"We know he had gone for a swim at the beach of Agios Nikolaos, but because he likes hiking and the area he would walk back.
"Some witnesses said that he was seen returning to Pedi and talking to another person.
"All of these are testimonies that are being investigated at the moment.
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Police said they had been alerted to the missing Briton on Thursday.
A policeman said the search so far has focused on the area between the beach of Ayios Nikolaos, where Mosley was last seen, and the resort of Pedi where the famous physician was staying with his wife.
A community Facebook group on Symi shared a photo of Dr Mosley wearing a blue polo shirt a cap and sunglasses, appealing for information.
The post reads: "Have you seen this man? He set off to walk back from St Nick's at about 13.30 and failed to make it home.
"His friends are concerned as it is 6 hours since they last saw him.
"His name is Dr Mike Mosley and he is a familiar face for many British people as he has appeared on the BBC.
"The police and coast guard have been informed EMAK, the island's rescue team, is also involved."
Senior Police Spokesman Constantina Dimoglidou told the Mail the search for the missing doctor is ongoing.
She said: "He was at the beach of Ag. Nikolas with another couple when he decided to go back to his home in the area of Pedi of Symi.
"It was around 1.30pm and he forgot his phone at the beach. Any and every attempt to track him down has not produced any result.
"We have now asked the fire brigade to assist in the operation in the case that he may have slipped, tripped, fallen, even bitten by a snake, remaining injured somewhere.
"There is just no trace of him. None whatsoever and that means that for us at least, every potential scenario is open and being investigated."
Dr Mosley is best known for hosting the BBC podcast Just One Thing.
He has also appeared on This Morning and The One Show.
The 67-year-old broadcaster did the Channel 4 show Michael Mosley: Who Made Britain Fat? and was part of the BBC series Trust Me, I'm A Doctor.
He also lived with tapeworms in his guts for six weeks for the documentary Infested! Living With Parasites on BBC Four.
