NINGBO (China) • Two days before they sought asylum in South Korea, the North Korean waitresses in the Chinese coastal city of Ningbo shopped for backpacks at a nearby store and paid relatively expensive full prices.

"I asked them 'Are you going on a trip?', and they said 'Yes'," said one of the workers at the store, who declined to give his name. "They seemed happy."

Two days later, 12 of the restaurant's waitresses and one male manager arrived in Seoul, the South Korean capital, in the biggest mass defection case involving North Koreans in several years.

How they planned and executed their trip remains a mystery.

South Korea has only said it has admitted 13 defectors, North Korean restaurant workers who arrived on April 7, on humanitarian grounds.

China said a group of 13 North Koreans used valid passports to leave the country normally on April 6, but did not say where they went.

In Ningbo, shopkeepers nearby considered the Ryugyong North Korean restaurant and its pretty but secretive waitresses a curiosity. The restaurant, now closed, sits on a newly developed pedestrian street for tourists that opened for business in late September last year.

An employee of the company that manages the vintage-looking grey brick and wood buildings that line the pedestrian street, including the Ryugyong, said the workers were very secretive and generally only seen outside when they were coming to and from work.

"They were under military-like management and not free to go anywhere," she said.

North Korea on Tuesday accused South Korea of kidnapping its citizens and demanded their repatriation. It said the South's intelligence agents "lured and abducted" the 13 North Koreans by using "all sorts of appeasement, deception and gimmicks".

"Unless they apologise for the hideous abduction and send those abductees back, they will face unimaginable serious consequences and severe punishment," a spokesman for the North's Red Cross Society, which is controlled by the government, was quoted as saying by the official Korean Central News Agency.

The North Korean government is believed to select loyal and relatively affluent citizens to be sent abroad as workers in the assumption that they would be less vulnerable to foreign influence.

The 13 defectors are children of North Korean party and administration elites, according to Daily NK, a website based in Seoul, which quoted sources within the North.

On Tuesday, North Korea did not hide its discontent with Beijing, saying that it knew "which country connived" to enable the group's defection.

REUTERS, NEW YORK TIMES