Georgia | A South Korean charter plane arrived in Atlanta on Wednesday to take home Korean workers detained in an immigration raid in Georgia last week.

Its planned return the same day was cancelled, and South Korea's Foreign Ministry later said the flight would take place Thursday at noon, without giving further details.

A total of 475 workers, more than 300 of them South Koreans, were rounded up in the September 4 raid at the battery factory under construction at Hyundai's sprawling auto plant.

US authorities released video showing some being shackled with chains around their hands, ankles and waists, causing shock and a sense of betrayal among many in South Korea, a key US ally.

South Korea's government later said it reached an agreement with the US for the release of the workers.

Workers expected to be brought back home after days of detention South Korean TV footage showed the charter plane, a Boeing 747-8i from Korean Air, taking off at Incheon International Airport, just west of Seoul, and it landed in Atlanta on Wednesday morning.

The Foreign Ministry said the plane was not able to depart from the US the same day, as South Korea wished, due to an unspecified reason involving the US side.

During a visit to Washington on Wednesday, South Korean Foreign Minister Cho Hyun met US Secretary of State Marco Rubio and told him that his country's people were left with “big pains and shocks” because the video of the workers' arrests was publicly disclosed, his ministry said in a statement.

Cho called for the US administration to help the workers leave as soon as possible — without being handcuffed — and to make sure they do not face problems in future reentry to the US, the statement said.

The workers were being held at an immigration detention centre in Folkston, in southeast Georgia. South Korean media reported that they would be freed and bused 460 kilometres to Atlanta to take the charter plane. Three empty buses were parked at the detention centre.

South Korean officials said they have been negotiating with the US to win “voluntary” departures of the workers, rather than deportations that could result in making them ineligible to return to the US for up to 10 years.

The workplace raid by the US Homeland Security agency was its largest yet as it pursues its mass deportation agenda. The Georgia battery plant, a joint venture between Hyundai and LG Energy Solution, is one of more than 20 major industrial sites that South Korean companies are currently building in the United States.

Many South Koreans view the raid as a source of national disgrace and remain stunned by it. Only 10 days earlier, President Lee Jae Myung and US President Donald Trump held their first summit in Washington, on August 25. In late July, South Korea also promised hundreds of billions of dollars in US investments to reach a tariff deal.

Experts say Seoul is not likely to take any major retaliatory steps against the US, but the raid could become a source of tensions between the allies.

South Korea calls for improvement in US visa systems US authorities said some of the detained workers had illegally crossed the US border, while others entered legally but had expired visas or entered on visa waivers that prohibited them from working.

But South Korean experts and officials said Washington has yet to act on Seoul's yearslong demand to ensure a visa system to accommodate skilled Korean workers, though it has been pressing South Korea to expand industrial investments in the US.

South Korean companies have been relying on short-term visitor visas or Electronic System for Travel Authorization to send workers who are needed to launch manufacturing sites and handle other setup tasks, a practice that had been largely tolerated for years.

LG Energy Solution, which employed most of the detained workers, instructed its South Korean employees in the US on B-1 or B-2 short-term visit visas not to report to work until further notice and told those with ESTAs to return home immediately.

During his meeting with Rubio, Cho proposed the creation of a joint South Korea-US working group to introduce a new visa category for South Korean workers, according to his ministry.

Cho met the previous day with representatives of major Korean companies operating in the US including Hyundai, LG and Samsung. Cho told them South Korean officials are in active discussions with US officials and lawmakers about possible legislation to create a separate visa quota for South Korean professionals, according to the ministry.

Trump said this week that the workers “were here illegally” and that the US needs to work with other countries to have their experts train US citizens to do specialised work such as battery and computer manufacturing.

Atlanta immigration attorney Charles Kuck, who represents several of the detained South Koreans, told The Associated Press that no company in the US makes the machines used in the Georgia battery plant.

So they had to come from abroad to install or repair equipment on-site — work that would take about three to five years to train someone in the US to do, he said.

The South Korea-US military alliance, forged in blood during the 1950-53 Korean War, has experienced ups and downs over the decades.

But surveys have shown a majority of South Koreans support the alliance, as the US deployment of 28,500 troops in South Korea and 50,000 in Japan has served as the backbone of the American military presence in the Asia-Pacific region.

During a Cabinet Council meeting on Tuesday, Lee said he felt “big responsibility” over the raid and expressed hopes that the operations of South Korean businesses will not be infringed upon unfairly again.