South Korean President Lee Jae-myung said on Thursday that a massive US immigration raid on a Hyundai-LG battery factory site in Georgia was "bewildering" and could have a chilling effect on future investment.

Seoul is expecting hundreds of workers detained during last week's raid in the US state of Georgia to be released from detention on Thursday and flown home by Friday on a chartered Korean Air Boeing 747-8I that seats more than 350 passengers. South Koreans made up the majority of the 475 people arrested.

Lee blamed the raid on "cultural differences" saying that in South Korea, American nationals teaching English while on a tourist visa were not seen as "a serious issue".

After the detentions, South Korean companies "can't help but question whether setting up a plant in the US is worth the potential risks," Lee said.

"This could have a significant impact on future investment decisions, particularly when evaluating the feasibility of direct operations in the US," he added.

Many South Korean companies have relied on bringing in their own workforce during project development periods, with industry sources saying it is common practice to use visa workarounds to bring in skilled labour and avoid project delays.

Lee said that for South Korean companies "when setting up facilities, equipment and factories, skilled technicians are essential".

"Someone has to install the machinery, and the necessary workforce simply doesn't exist locally in the US," he said, adding that the companies had long relied on bringing in their engineers for short-term periods to train local workers. "But now, even that basic request is being rejected."

Lee said Seoul was negotiating with Washington "to ensure that visa issuance for investment-related purposes operates normally". This could include "securing additional quotas" or even creating a new visa category, he said, adding that he trusted the "US side will find a solution".

The raid highlights lopsided priorities in the Trump administration, which is "actively bringing in large-scale production facilities while neglecting to train local workers," said Kim Dae-jong, professor of business at Sejong University. "As a result, South Koreans are having to train the local workforce. Logically, the two sides' workers should be allowed to work together, not be hindered from doing so."

The repatriation was briefly delayed by Trump asking whether the workers should remain stateside, a Seoul foreign ministry official in Washington said.

Washington suspended the repatriation as "Trump had asked whether the detained South Korean workers, all of whom were skilled professionals, should remain in the United States to continue working and training American staff," the official said.

However, South Korea's Foreign Minister Cho Hyun said that "given the workers' shock and exhaustion, it would be best for them to return home first and then re-enter the US for work later". (AFP)