Police say a body believed to be that of missing TV presenter Michael Mosley has been found on a Greek island.

A police spokesman, who spoke on condition of anonymity today (tonight AEST) because of an ongoing investigation, said the body was found on a rocky coast by a private boat and that formal identification was pending.

The British television presenter disappeared while on holiday on the island of Symi, which is on the eastern side of the Aegean Sea and about 6.5 kilometres from Turkey.

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A search and rescue operation has been under way since Wednesday.

Mosley, 67, is believed to have gone for a coastal walk along Saint Nicholas Beach on Wednesday afternoon while on holiday on the island, which is a popular destination for hikers.

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 in a week while eating healthily on the other five.

Rescuers were earlier focusing their search efforts on a maze of tunnels known as 'The Abyss'.

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At least 100 rescuers and volunteers, including a helicopter, were scouring the area between Agios Nikolaos and the island's main town in search of the 67-year-old.

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 were on their way to the island to aid in the search. 

He later introduced the Fast 800 diet, a rapid weight loss program, and has made a number of films about diet and exercise.

Mosley often pushed his body to extreme lengths to see the effects of his diets.

He lived with tapeworms in his guts for six weeks for the BBC documentary Infested! Living With Parasites.

– Reported with Associated Press