The runners had to negotiate a jungle route 100 miles (160 km) long on the Thailand-Malaysia border.
Adding colour to the event were runners in fancy attire, including one man wearing a "Forrest Gump" costume comprising a plaid shirt, khaki pants and a red cap.
The contestant successful matched the look of an iconic movie character in the 1994 hit film "Forrest Gump", in which the low-IQ protagonist becomes famous for his running campaign.
The photo of the runner taken at the starting line in Betong district of Yala province has been liked and shared on the Facebook page of the organiser more than 10,000 times.
Organiser UTMB World Series called the route “Betong 160”, starting at Betong Mongkhonrit Tunnel and terminating at Betong Clock Tower.
UTMB had advertised the event as a “run through the refuge tunnel, to the delight of the beautiful sky and sea of mist of Gunung Silipat, Jaroh Ganga, Kapae Hulu and Kuan Toh Ni scenic point”.