A search has been mounted for British explorer Benedict Allen, whose family say has gone missing during an expedition to Papua New Guinea.
The 57-year-old was travelling on his own to try to find the reclusive Yaifo tribe, whom he first met 30 years ago.
His sister says she was expecting to hear from him by Monday – and he hasn’t taken planned flights home.
A helicopter pilot, who dropped Mr Allen off several weeks ago, is trying to find him, the BBC has learned.
Our security correspondent Frank Gardner, who recently travelled through Papua New Guinea with Mr Allen for a BBC documentary, said he understood the pilot was tracking Benedict’s route from his starting point in a remote place called Bisoria.
They have spoken to local police chiefs, and were looking to locate him by helicopter and get him out, our correspondent said.
He added that the former UK high commissioner to Papua New Guinea, David Gordon-Macleod, said “huge areas of the country have no mobile coverage”, meaning that even if Mr Allen had reached a village, he is likely to still be out of contact with the outside world.
Mr Allen’s older sister, Katie Pestille, said it was “out of character” for him to miss his scheduled flight out of Papua New Guinea to Hong Kong.
“It’s ghastly,” she told BBC Radio 4’s Today programme.
“For everybody else, it’s very exciting – all the expeditions and all the things he does, but for his sister and his wife, it’s more of a worry,” she explained.