Authorities are conducting searches for the missing tourists, who were kayaking down the Balandkiik River when they disappeared, RIA Novosti reported.
The missing men have been identified as Ben Luck, Cooper Lambla, Matt Klema, Nate Klema and Charles King.
They set off an emergency signal using a GPS tracking device on Monday. At the time, their location was inside Tajikistan's Pamir National Park, a wild area home to many high mountain peaks.
A helicopter rescue team found a broken kayak in the area Oct. 1, and, shortly after, another emergency signal was set off six miles away.
The men were likely retracing their path, the GPS coordinates indicate.
The Americans had spent two months traveling in Asia and did not plan to return to the United States until December.
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