Vietnamese army cameramen recalled the horrific scenes as they passed through the barbed wire gates of Pol Pot's S-21 torture centre in Cambodia's capital 30 years ago.

"We had to use masks and perfume to bear the stench as we walked into the centre," said Dinh Phong, a member of an army film crew covering Hanoi's toppling of the Khmer Rouge regime that was blamed for the deaths of 1.7 million people.

They found five emaciated children, one of whom later died, hiding under piles of prisoners' clothing in the Phnom Penh school where at least 14,000 people were tortured and killed.

"They were all naked. Their bodies marked by mosquito bites," Mr Phong, 70, told reporters on the eve of the first trial of Pol Pot's surviving henchmen by a United Nations-backed tribunal.

The black-and-white footage of the swollen, maggot-infested bodies in S-21, some of them still shackled, was taken a few days after Pol Pot's fighters were driven out of the capital in January 1979.

The film is expected to figure prominently in the trial of former S-21 chief Kaing Guek Eav, also known as Duch, which formally began yesterday with procedural motions.

Ho Van Tay, who led the Vietnamese film crew, said the 16-mm footage showed the axes, spades and electrical wires used to torture and later kill inmates.

"We had to step around swollen, worm-infested corpses with shackles on their ankles," the 75-year-old said.