Sheltering in the shade of a bus repurposed into a mobile museum, Mean Loeuy tells a group of children about the hell he went through in a Khmer Rouge labour camp.

"At the beginning we shared a bowl of rice between 10 people," recounts the 71-year-old man who lost more than a dozen family members during Cambodia's bloodiest era.

"By the end, it was one grain of rice with a splash of water in the palm of our hands," he says, describing the camp as "like a prison without walls."