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LONDON — A British explorer has vanished during an expedition to find an indigenous tribe in Papua New Guinea.

Benedict Allen Calyx/Rex / Shutterstock via AP file

Benedict Allen, 57, was dropped into the rainforest by helicopter last month. He was travelling alone and wasn't carrying a satellite phone or any GPS devices.

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He was scheduled to catch a flight out of the country on Monday but did not show up, his management agency confirmed Wednesday.

Allen was hoping to make contact with the reclusive Yaifo tribe, which he had encountered in a mountainous area some 30 years ago.

The explorer is well-known in the U.K. for TV documentary programs in which he travels to remote parts of the planet without any form of modern technology.

On Oct. 11, Allen tweeted a picture of himself along with his gear with a caption saying he was heading to a London airport.

Marching off to Heathrow. I may be some time (don't try to rescue me, please - where I'm going in PNG you won't ever find me you know...) pic.twitter.com/BmH1DKdheS — Benedict ALLEN (@benedictallen) October 11, 2017

In a blog post published in September, Allen also warned that he would not have an obvious means of returning to the outside world — which he said was “somewhat worrying, especially at my advanced age.”

He explained that the aim of his trip to Papua New Guinea was to create a brief record of how the tribe lives and possibly track down some of the people he met in the 1980s.

The explorer said he was unsure how members of the Yaifo tribe would react to him or if he would even make it to where he believes they are located due to the “rather treacherous terrain.”

“Last time, the Yaifo 'greeted' me with a terrifying show of strength, an energetic dance featuring their bows and arrows,” he wrote. “On this occasion who knows if the Yaifo will do the same, or run off, or be wearing jeans and T-shirts.”