The son of a south London man who is missing in Jamaica has said "time is ticking" to find him alive.
Robert Dyer went missing on Sunday when he was out walking in a wooded area near St Elizabeth in the south-west of the Caribbean island.
His son, Lewis Dyer, has called for more resources to be put into the search, including drones with thermal imaging to help scour the dense bush.
He said: "I can't stress how time-critical this is."
Robert, who is from Lewisham, last made contact with his family after he got lost on his walk.
Clara Beasley, Lewis's wife, told BBC London: "Overnight on Sunday he called his brother to say he had lost his way."
She said he called his wife Anne on Monday when the 60-year-old sounded "disoriented" and was "severely dehydrated".
The family have been unable to make contact since.
More than 250 people were with the search operation on Tuesday, according to local media reports.
Lewis said: "We have a family group chat where we're trying to organise millions of different things. Some of us are in Jamaica, the UK, US and Spain. None of us have slept."
He said the Jamaican police and army had been helping in the search, including with a helicopter and search-and-rescue dogs.
"The locals are the heroes," Lewis said. "They have given up their time to search and walk up and down in tough terrain. They don't even know my dad, they're just amazing people just trying to help."
'We just hope he's alive'
On Wednesday night volunteers found Robert's trekking stick, which Lewis said had allowed them to narrow the search area.
He said he wanted thermal imaging drones to be used overnight to search for his father and has called on authorities or anyone with the equipment to assist in this.
"At night-time it's practically impossible for most people to go out and it's probably quite dangerous," Lewis said.
He added: "We don't know what state he is going to be in. We just hope he's alive."