The chief Khmer Rouge torturer has gone on trial in Cambodia for crimes against humanity.

Kaing Guek Eav, known as Duch and ex-commandant of the notorious S-21 prison, sat impassively in a blue shirt as a judge read the opening statements in court.

It is the first case involving a senior figure of Pol Pot's regime three decades after the end of an administration that is blamed for 1.7m deaths.

Hundreds of victims of Khmer Rouge atrocities lined up to get into court, but the proceedings are mostly procedural, with the main trial starting in March and a verdict due by September.

Duch, now a born-again Christian, expressed remorse on the eve of his trial.

The court has been set up to prosecute those most responsible for the 1975-79 reign of terror, one of the darkest chapters of the 20th century.

The trial is a landmark for the strife-torn country where nearly every family lost someone under the Khmer Rouge.

'This is the day we have waited for for 30 years. But I don't know if it will end my suffering,' said Vann Nath, an artist who managed to get a seat near Duch.

He was one of only a handful of people to survive S-21. He was saved because he was chosen to paint portraits of leader Pol Pot.

The trial ends a decade of delays at the Cambodian-UN tribunal due to wrangling over jurisdiction and cash, but critics say the court's integrity is threatened by allegations of corruption and political interference over who to prosecute.

Pol Pot's death in 1998 was followed by a formal Khmer Rouge surrender, which helped to usher in a decade of peace and stability.