The search for British TV presenter and healthy living advocate Michael Mosley entered its third day on the Greek island of Symi on Friday following his disappearance after setting out on a lone coastal walk in searing heat.

The veteran doctor, known for endorsing fasting and for tips on sleep and diet, was last seen at 1:30 p.m. (1030 GMT) on Wednesday when he set out on a short stroll along a rocky path between Agios Nikolaos beach and the village of Pedi, police officials said.

Police, the fire brigade, coast guard and volunteers were searching for Mosley on and offshore the small mountainous island in the eastern Aegean, using a helicopter, drones and a rescue dog as temperatures hit 40 degrees Celsius (104 Fahrenheit).

A Reuters reporter saw more policemen arriving to assist on Friday, but fears were growing that Mosley, 67 and a staple on British TV for two decades, had not survived.

He did not have his mobile phone with him, which made tracing him more difficult.

“Probably he fell into the sea and washed away, or something else has happened,” Symi Mayor Lefteris Papakalodoukas told Reuters. “It’s impossible to be where the searches are taking place. It is a small area and has been thoroughly searched.”

A security team from the nearby island of Rhodes was expected to arrive and investigate on Friday, a police official said.

“So far, we don’t have evidence of what may have happened, whether it is an accident … or something else,” said a senior police official who declined to be named.

Police were looking into reports that he had spoken to locals halfway through his walk.

Symi is sparsely populated, about 10 miles long with 2,500 residents. Its remote beaches, some of which are accessible only by boat, were filled with sun-bathing tourists on Friday.

Mayor Papakalodoukas doubted foul play.

“We have zero crime on our island. We are a small community and we are all upset,” he said.

Mosley has appeared on British programmes including the BBC series Trust Me, I’m a Doctor, the BBC’s The One Show and ITV’s This Morning.

He popularised the 5:2 diet, which endorses intermittent fasting.

There were dozens of expressions of concern among colleagues and friends on social media. The story was on the front page of the Daily Mail newspaper, where Mosley is a columnist.