China repatriates about 5,000 North Korean refugees each year even though they often face harsh punishment on their return, South Korean activists said Tuesday.

North Koreans who make the risky journey across the border into China only to be returned to their homeland face torture, imprisonment and even execution in extreme cases, the activists said.

"It is believed that the number of repatriated North Korean refugees reaches 5,000 per year," said Kim Suk-Woo, a former vice unification minister who now works for a rights group in Seoul.

At a forum on the issue he and other activists distributed a petition signed by 100 former South Korean ambassadors, calling on China to halt the repatriations which they say violate the refugee rights under international conventions.

China treats North Koreans as economic migrants rather than refugees.

More than 21,700 North Koreans have fled their impoverished homeland for South Korea since the 1950-1953 war, the vast majority in recent years.

Almost all escape on foot to China, travel surreptitiously to Southeast Asia and then eventually seek resettlement in South Korea.

"The international community is not begging China for merciful treatment of the refugees, but asking her to duly abide by international laws and obligations," Kim said.

Many orphans born of North Korean refugees and Chinese fathers are in a "miserable" situation without proper care or basic education, he said.

They are abandoned in the streets if their mothers are arrested and sent back, Kim said.

"Punishment back in North Korea is really harsh and beyond your imagination," said Lee Myung-Sook, a female refugee who settled in South Korea in late 2008 after escaping through Thailand.

Lee, 43, fled to China in 2003 and was sold by brokers to a disabled Korean-Chinese man. She escaped three years later but was arrested by China and repatriated.

Female refugees housed in a Chinese camp while awaiting deportation face torture and beatings, she said, claiming some inmates were sexually harassed or raped by Chinese soldiers.

On her return, Lee said, she was detained in a political prison camp for six months before escaping again to China in 2006.

"I was beaten badly, although I was pregnant," Lee said, adding one prisoner died in the camp almost every day.