A UN-MANDATED investigator has spotlighted "unspeakable atrocities" inflicted on political camp prisoners in North Korea, citing testimony from survivors who saw babies drowned or had to survive by eating lizards.

Retired Australian judge Michael Kirby challenged the secretive Stalinist country to come clean about its record, telling the UN Human Rights Council he aimed to draw up a list of violators within North Korea's regime.

Mr Kirby is at the helm of a landmark commission of inquiry on North Korea set up in March by the council, the UN's top human rights watchdog.

North Korea has refused to co-operate with the commission, which has spent recent months gathering evidence in South Korea and Japan from North Korean defectors and other victims.

"Testimony heard thus far points to widespread and serious violations in all areas," Mr Kirby told the council on Tuesday, to which he is due to deliver a full report next year.

He said the evidence, both sobering and heart-rending, had "given a face and voice to great human suffering".

"The commission listened to political prison camp survivors who suffered through childhoods of starvation and unspeakable atrocities, as a product of the 'guilt by association' practice, punishing other generations for a family member's perceived political views or affiliation," he said.

Among the stark testimony was that from a man imprisoned from birth, who lived on rodents, lizards and grass, and witnessed the public execution of his mother and brother; from a woman who saw a fellow inmate forced to drown her own baby in a bucket; and from a man obliged to burn the corpses of starved inmates and scatter their ashes on fields.

Mr Kirby also spotlighted torture and sexual violence, detention for watching foreign soap operas or having religious beliefs, kidnapping citizens of South Korea and Japan, massive malnutrition, and the total control by the regime's propaganda apparatus.

North Korean diplomat Kim Yong-ho hit back, telling the council the evidence was "fabricated and invented by forces hostile" to his country, singling out Washington, Tokyo and Brussels.

North Korea has claimed such testimony is slander from "human scum", but Mr Kirby shot that down.

"An ounce of evidence is worth far more than many pounds of insults and baseless attacks. So far, however, the evidence we have heard has largely pointed in one direction - and evidence to the contrary is lacking," he said.

North Korea has long been subject to international sanctions over its nuclear program.

Mr Kirby said it was also essential to ensure full accountability for human rights violations.

"We will seek to determine which state institutions and officials carry responsibility for gross human rights violations proved to have been committed," he said.

But he cautioned that his commission was "neither prosecutor nor judge" and responsibility for action lay with the international community.