North Korea's famine in the 1990s unleashed a Darwinian struggle for survival that swiftly eliminated many of the most vulnerable in an already sharply stratified society, a UN panel heard Thursday.

"People are treated without dignity in North Korea -- and in some cases like sub-humans," said Ji Seong-Ho, who was 14 when he lost his hand and left leg trying to steal coal from a moving train during the famine years.

Ji, now 31, was one of a number of North Korean defectors called to testify before a UN Commission of Inquiry into human rights in North Korea that is currently holding hearings in Seoul.

The North, which strongly denies allegations of rights abuses, has refused to recognise the commission and barred its members from visiting the country.

Ji said mentally and physically disabled people faced widespread social and official discrimination in North Korea, where they are judged as being of "no use" to society.

"When I was young, before my accident, I admit I used to make fun of adults with disabilities," he said.

During the 1994-98 famine, which saw hundreds of thousands starve to death, ordinary North Koreans had to focus all their energies on scavenging to stay alive.

Food was so scarce that there was little to share and those who could not fend for themselves -- the very young, the elderly, the disabled -- were at particular risk.

"We had disabled people in our town, but by the time the food situation had begun to improve slightly in the late 1990s, we didn't see them any more, meaning they must have died," Ji said.

In March 1996 he was attempting to steal coal from a train to sell for food when he fell under the wheels, severing his left hand and leg.

"It was only then I realised how loud I could scream," said Ji, who was taken to hospital and operated on without morphine or general anaesthetic .

Unable to walk without crutches and with no job prospects, Ji managed to cross the border illegally into China in 2000 in an effort to find food for his family.

Police caught him on his return, held him for a week and, Ji said, beat him severely.

"They shouted at me, calling me a cripple and saying that I brought shame on North Korea by looking the way I did," he said.

Ji finally escaped for good in 2006 and settled down in South Korea, where he now studies law and speaks publicly about life in the North.

Also testifying to the commission on Thursday was Kim Hyuk, 32, who at the age of seven after his mother's death became a "ggotjebi" -- the North Korean term for street children, mostly orphans, who beg, scavenge and steal to survive.

"When I started that life, people were willing to give us food, but obviously that changed when the famine came," Kim said.

As children began to die in the streets, Kim said special police units were set up to round up all the ggotjebi and send them to shelters and orphanages, where many still died of starvation.

"There was no food at all," Kim said of the orphanage where he spent three years. "Just powdered corn husk which left you constipated. I caught and ate lizards, snakes, rats and grass."

Of the 75 children in the orphanage, 24 died.

"The officials said it was due to disease, but it was malnourishment. They became too weak to walk. Their bodies were buried in the backyard," Kim said.

Kim ran away but was then arrested for making smuggling runs across the border with China and served 20 months in a re-education camp where the conditions were as bad as the orphanage.

"There were 24 of us who entered the camp on the same day. Only two survived," he said.

Released from prison, Kim sneaked across the Tumen River into China in December 2000 and arrived the following year in Seoul, where he now lectures on his experiences on behalf of the Unification Ministry.