One of the last remaining survivors of a notorious Tuol Sleng prison gave his long-awaited testimony Monday at Cambodia's war crimes tribunal, weeping as he described how he and other inmates ate insects to stave off starvation.

Vann Nath, a survivor from the Tuol Sleng prison during the Khmer Rouge regime, is seen on a television screen at a court press centre during his testimony at the UN-backed tribunal Monday in Phnom Penh, Cambodia. (Heng Sinith/Associated Press)"The conditions were so inhumane and the food was so little," Vann Nath told the UN-backed tribunal in Phnom Penh, tears streaming down his face.

"I even thought eating human flesh would be a good meal."

Nath testified he only survived his imprisonment at the prison and was spared torture there because the prison's chief, known as Comrade Duch, liked his paintings of the Khmer Rouge leader, Pol Pot.

"I survived because Duch felt good when he walked into my workshop," Nath said of the ailing man currently facing trial, whose real name is Kaing Guek Eav.

Duch, 66, was the senior Khmer Rouge official in charge of the infamous prison between 1975 and 1979. Up to 16,000 men, women and children were tortured under his command and later taken away to be executed. Only seven people, among them Nath, are known to have survived the prison.

Duch is the first senior Khmer Rouge figure to face trial and the only one to acknowledge responsibility for his actions. He watched impassively Monday as Nath testified.

In this image photographed from TV footage, former Khmer Rouge prison commander Kaing Guek Eav, also known as Comrade Duch, reads a statement earlier this year at Cambodia's war-crimes tribunal. (APTN/Associated Press)Taken to Tuol Sleng in 1977, Nath escaped from the prison in 1979 as the Khmer Rouge regime collapsed after neighbouring Vietnam invaded Cambodia. Nath became one of Cambodia's most renowned artists and has depicted the prison's victims and the horrors they faced in his paintings.

During his testimony, Nath, 67, told the tribunal he was fed twice a day, with each meal consisting of three teaspoons of rice porridge. Prisoners were kept shackled and ordered not to speak or move.

"We were so hungry, we would eat insects that dropped from the ceiling," Vann Nath said. "We would quickly grab and eat them so we could avoid being seen by the guards."

"We ate our meals next to dead bodies, and we didn't care because we were like animals," he added.

Duch is charged with crimes against humanity and is the first of five defendants scheduled for long-delayed trials by the UN-assisted tribunal. The four other senior Khmer Rouge figures are expected to face trial next year.

Duch has previously testified that being sent to Tuol Sleng was tantamount to a death sentence and that he was only following orders to save his own life.

The regime's radical policies caused the deaths of an estimated 1.7 million people nationwide by execution, overwork, disease and malnutrition.

With files from The Associated Press