The Kaesong Industrial Complex, the last bastion of inter-Korean cooperation amid escalating military tension, is facing its worst crisis since the project started in 2003.
Pyongyang on Wednesday closed the border to South Korean workers and vehicles at the industrial park, prompting Seoul to warn that it could resort to military action should the safety of its citizens there be compromised.
But thirty-three South Koreans who work at the complex returned to the South in the afternoon. Some said North Koreans there looked unusually tense.
"Workers who normally wear civilian clothes wore military uniforms and patrols were strengthened," said one worker.
The North also replaced civilian customs staff with soldiers and customs checks took longer than usual. Another worker said that there were even armored vehicles on standby.
"The demeanor of North Korean workers appears to have changed overnight," said another. "They were colder than usual and didn't smile." And a fourth reported, "Inter-Korean relations are a problem, but we're very concerned that we could lose our business."
Some said their co-workers who remain in the complex wonder whether they would be allowed to return or be taken hostage. Around 800 South Korean workers remain.
"If parts or food fail to reach the North for two to three days, the assembly lines will stop running and workers will starve," said one worker.
But others denied anything has changed much. "The atmosphere remains the same," said one South Korean who works for a textile firm there. "We went through the crisis after the sinking of the Cheonan, and I couldn't see any change among the workers there."
Around 80 Korean and foreign journalists gathered in front of the South Korean checkpoint at the border in Paju just north of Seoul on Wednesday, but most of the returning staff declined requests for interviews.
An association of South Korean businesses in the complex convened an emergency meeting Wednesday. "Our greatest concern is the safety of our workers there," said Han Jae-kwon, the head of the association. "We urge North Korea to allow components and food to be sent in."
A staffer with the association said South Korean companies stockpiled enough food to last for two weeks and a month's worth of raw materials, but the amount differs from company to company.
Meanwhile, residents of Paju just south of the heavily fortified border, spent a tense afternoon. "There were no irregular movements along the border, but many of us are worried since we are very close to the frontlines," said one resident of Freedom Village.
The number of tourists visiting the border also dropped significantly, from an average of 2,500 on a normal day to just 1,000 on Wednesday.