South Korean companies will be "very hesitant" about investing in the US following a massive immigration raid at a Hyundai plant in the state of Georgia last week, President Lee Jae Myung has said.

More than 300 South Koreans who were arrested in the raid have now been released from detention and are due to return home on Friday after having their release delayed by more than a day.

Their departure was delayed because of an instruction from the White House, Lee added.

President Donald Trump ordered the pause to check whether the workers were willing to remain in the US to continue working and training Americans, according to a South Korean foreign ministry official.

Lee, who was speaking at a news conference to mark the first 100 days of his presidency, said "the situation is extremely bewildering," while noting it is common practice for Korean firms to send workers to help set up overseas factories.

"If that's no longer allowed, establishing manufacturing facilities in the US will only become more difficult... making companies question whether it's worth doing at all," he added.

Seoul is negotiating with Washington on visa options for South Korean workers "whether that means securing [higher] quotas or creating new visa categories", Lee said.

"I think the US will address this if they see it as a practical necessity."

The BBC has contacted the White House for comment.

Last week, US officials detained 475 people - more than 300 of them South Korean nationals - who they said were working illegally at the battery facility, one of the largest foreign investment projects in Georgia.

LG Energy Solution, which operates the plant with Hyundai, said that many of its employees who were arrested had various types of visas or were under a visa waiver programme.

A worker at the plant spoke to the BBC about the panic and confusion during the raid. The employee said the vast majority of the workers detained were mechanics installing production lines at the site, and were employed by a contractor.

South Korea, a close US ally in Asia, has pledged to invest tens of billions of dollars in America, partly to offset tariffs.

Media in the country have described the raid as a "shock," with the Dong-A Ilbo newspaper warning that it could have "a chilling effect on the activities of our businesses in the United States".

The Yonhap News Agency published an editorial on Thursday urging the two countries to "cooperate to repair cracks in their alliance".

The timing of the raid, as the two governments engage in sensitive trade talks, has raised concern in Seoul.

The White House has defended the operation at the Hyundai plant, dismissing concerns that the raid could deter foreign investment.

On Sunday, US President Donald Trump referenced the raid in a social media post and called for foreign companies to hire Americans.

The US government would make it "quickly and legally possible" for foreign firms to bring workers into the country if they respected its immigration laws, Trump said. (BBC)