New CCTV of a man believed to be missing TV and radio presenter Michael Mosley on the Greek island of Symi has been seen by the BBC.

The footage appears to show one of the last-known sightings of the 67-year-old walking with an umbrella next to the marina in the village of Pedi on Wednesday, heading towards rocky hills.

The mountainous terrain is described as "not easy" by those involved with the search.

Dr Mosley, known for his TV programmes and BBC Radio 4's Just One Thing podcast, vanished four days ago while on holiday - after leaving a beach on foot.

A search and rescue operation, involving helicopters and drones, continues.

The new image appears to show the man in good form and walking steadily, an unnamed police officer told BBC News.

This is believed to be one of the last two CCTV sightings of the man with the umbrella before he left the village.

Earlier on Saturday, firefighters started searching a 4 mile (6.5km) radius over a mountainous area that is surrounded by sea.

Asked if there had been any sign of Dr Mosley, he said there has been "nothing".

One theory that has emerged was that Dr Mosley was trying to take a much longer route than previously thought, passing over miles of exposed hillside.

Dr Mosley's accommodation was in the main town about 1 mile from Pedi.

Dr Mosely's movements have been pieced together from a series of CCTV images.

A man believed to be the broadcaster was seen on Pedi’s main street holding an umbrella about 20 minutes after leaving the beach.

A member of the rescue team described the search as a “race against time” and said he could be “anywhere”.

His four children have arrived on Symi to help with the search. His wife Dr Clare Bailey Mosley has also been searching the island joined by her British friends, Symi's mayor said.

All patrol boats, private boats and commercial boats near the island have been searching for Dr Mosley, Symi’s coastguard said, while police and firefighters have been using drones and a sniffer dog to try to locate the missing presenter.

Divers have been "looking into the water" with the help of the Hellenic Coast Guard.

Symi's mayor Eleftherios Papakaloudoukas said the search will continue until Dr Mosley is found.

He added he was unsure why the missing presenter would try to make a long, potentially arduous journey in such heat, but he hoped the presenter is found "safe and alive".

Greek police said Dr Mosley left his wife on the beach on Wednesday, before setting off on a walk to the centre of the island.

His phone was found where he was staying with his wife, who reported him missing, a police spokesperson told BBC News.

An appeal saying he was missing was posted on a local Facebook group on Wednesday, alongside a picture of Dr Mosley wearing a blue cap, polo shirt and shorts.

"Have you seen this man? He set off to walk back from [Agios Nikolaos beach] at about 13:30 and failed to make it home," it said.

Symi is part of Greece's Dodecanese island group and sits about 12 miles (19km) north-west of Rhodes. In the 2021 census it had a population of approximately 2,600 people.

The majority of its beaches are remote and people are advised to take boats to visit them.

Before moving into TV, Dr Mosley studied medicine in London and qualified as a doctor but for the last couple of decades has been working as a presenter, documentary maker, journalist and author.

He writes a column for the Daily Mail and his TV programmes also include Channel 4 show Michael Mosley: Who Made Britain Fat?

Dr Mosley has been an advocate for intermittent fasting diets, including the 5:2 diet and The Fast 800 diet.

His wife Clare Bailey Mosley, is also a doctor, author and healthy living advocate.

The couple recently appeared at the Hay Festival where Dr Mosley presented a special edition of Just One Thing.

Reacting to the "shocking news", his fellow Trust Me, I'm A Doctor co-star Dr Saleyha Ahsan said she was "praying he is found safe" and she feels "sick with worry".

On Thursday's edition of The One Show, presenter Alex Jones opened the programme by expressing concern that "our friend" had gone missing.

"Our thoughts are very much with his wife Clare and the rest of his family at this worrying time. We hope for more positive news," she added.

Wednesday 1330 local time (11:30 BST) - Dr Michael Mosley leaves his wife Clare on Agios Nikolaos beach and sets off on a walk

1350 - Man carrying umbrella is seen on CCTV in Pedi

1357 - Same man is seen again at Pedi's marina heading north-east

Thursday 1115 - Police are unable to find the presenter, so they inform Athens and request assistance from the Greek fire department

1400 - Greek fire services, with six firefighters and a drone team, arrive in Symi

1900 - Helicopter deployed to assist search

Friday - Divers join the search in the water around Symi

Saturday 0600 - Firefighters resume search for Dr Mosley

Additional reporting by Insaf Abbas in Symi and Andre Rhoden-Paul in London