A British explorer who went missing on an expedition to reach a remote tribe in Papua New Guinea has been seen alive and well, reports say.
Benedict Allen, who has no mobile phone or GPS device with him, was dropped by helicopter in the remote jungle three weeks ago.
He was hoping to reach the Yaifo, a tribe thought to be one of the last on Earth to have no contact with the outside world.
His friend, BBC security correspondent Frank Gardener, tweeted: "UK explorer @benedictallen has been sighted, 'alive and well' nr airstrip in Papua New Guinea after being reported missing while trekking."
UK explorer @benedictallen has been sighted, 'alive and well' nr airstrip in Papua New Guinea after being reported missing while trekking. pic.twitter.com/8neKeC9IGS— Frank Gardner (@FrankRGardner) November 16, 2017
Mr Gardener travelled to Papua New Guinea with Mr Allen twice last year.
Frank Gardner told BBC Radio 4's Today programme: "He has been reported alive and well.
"He's been sighted, we've had a second sighting of him now, tribal chiefs in the area that he went missing say that he has been sighted near an airstrip, that he's okay, that his health is fine, that he's requesting rescue.
"So efforts are now under way to try and bring him out.
"It's always possible that they could have made a mistake but I'm not aware of any other 57-year-old lanky British explorers that have gone missing in that area so let's hope that it isn't a false glimmer of hope but I think he's going to be okay."
Mr Gardener added: "He went looking for the Yaifo tribe, he went to visit them 30 years ago when hardly anybody had any contact with them at all, they initially charged him with bows and arrows."
Mr Allen had been expected to begin his journey home at the weekend but failed to make a flight to Hong Kong.
His wife Lenka Allen told the Daily Mail that their children - 10-year-old Natalya, Freddie, seven, and two-year-old Beatrice - were asking: "When's Daddy coming home?"
She said "everything possible" was going through her head, fearing that he had been bitten by a snake, become lost or contracted an illness.
But she added: "He does know a lot about the jungle."
In a blog post on his website in September, Mr Allen described the Yaifo as "one of the last people on the entire planet who are out of contact with our interconnected world".
"In October I'm hiring a helicopter to drop me off at the abandoned mission station, Bisorio - a forlorn place," he wrote.
"Last time the Yaifo greeted me with a terrifying show of strength, an energetic dance featuring their bows and arrows.
"On this occasion who knows if the Yaifo will do the same, or run off, or be wearing jeans and T-shirts traded eons ago from the old mission station."
He said he did not have an obvious means of returning home and either had to paddle down river for a week or so, or enlist the help of the Yaifo.
"Just like the good old days, I won't be taking a sat phone, GPS or companion. Or anything else much," he wrote.
"Because this is how I do my journeys of exploration. I grow older but no wiser, it seems."