Filming was delayed when actual squatters took up residence in the Chinese squatter village set. After their removal, filming resumed and the Chinese squatters stayed to watch. When the village is torched, crying and wailing can be heard. This wasn't from the Malay extras but from the real squatters who just lost their new home.
Because the UK government deemed the script to be prejudicial to British interests, it refused to cooperate. Therefore, all British troops were portrayed by Australian troops who were, at the time, running operations along the Malaysian-Thai border.
During a forced break in filming due to heavy rains, a Malay Bomoh, or shaman, was hired to predict when the rains would cease. His prediction was spot on and filming resumed.
Michael Keon, the author of the book the movie is based on, was the former brother-in-law of Ferdinand Marcos, former president of the Philippines. He was also reportedly a personal friend of Zedong Mao.
Capucine was cast as Dhana due to her romantic relationship with executive producer Charles K. Feldman. Her casting was initially opposed by William Holden, producer Karl Tunberg and director Lewis Gilbert. They were overruled by Feldman. Later in the shoot Holden began an affair with Capucine, much to the displeasure of Feldman.