Dr Michael Mosley: Divers and sniffer dogs join search for missing TV doctor

He told his wife and friends that he was walking back to the port where they were staying.

The journey should have taken no longer than an hour and experts say the most challenging part of the walk involves a climb of around 100 steps to a high point of around 50 metres.

On Wednesday morning, Mosley, his wife and another couple took a boat taxi from Symi Port up the coast.

The group stopped at St Nikolas beach where the TV doctor went for a swim in the sea before deciding to walk the 2.2 miles back home.

Once past the small coastal town of Pedi, the route to his holiday home involves main roads.

Police in Symi are working on the theory the father-of-four was bitten by a snake or became disoriented as temperatures surged to around 35C when he disappeared.

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According to a woman in Pedi, a person matching Mosley's description was spotted around 2.30pm near a bus stop and asking for directions.

"This woman said she saw him by the bus stop and she recognised him and at first we thought it was possible," a rescue official in Symi told MailOnline.

"The area was searched extensively with drones and dogs and a helicopter but we found nothing and now we are not so sure it was him.

"It is very strange and we just don't know where he is but we think the heat may have played a part as it was very hot that day."

Earlier today, CCTV footage appears to show the missing 67-year-old just 30 minutes after he set off for his coastal walk.

A helicopter was deployed to assist in the search at around 7pm local time (5pm BST) yesterday.

Officials described the temperature on the island as "unbearable" on the day he went missing.