US immigration authorities have raided a massive Hyundai factory in Georgia, leading to the arrest of 475 people, according to one of the agencies involved in the operation.

The 3,000-acre site, which was built by the Korean automobile manufacturer to make electric vehicles, had been operational for a year.

The Department of Homeland Security told the BBC that agents executed a search warrant due to allegations of “unlawful employment practices and other serious federal crimes”.

Most of those detained were Korean nationals, authorities said. The South Korean foreign ministry has expressed concern about possible “unjust infringement” of their rights while they are being held.

Hyundai Motor Company said it was “working to understand the specific circumstances” of the raid.

“As of today, it is our understanding that none of those detained is directly employed by Hyundai Motor Company,” it said in statement.

Hyundai’s production of electric vehicles at the sprawling site was not affected, Reuters reported. Its partner in its battery joint venture, South Korea’s LG Energy Solutions, had paused construction work at the site.

At a press conference on Friday, an official with the US Immigration and Customs Enforcement (ICE) said that a majority of the 475 people arrested were Korean nationals, but he could not give an exact number. They were being held at a facility in Folkston, Georgia, until the agency decided where to move them next.

“This in fact was the largest single-site enforcement operation in the history of homeland security investigations,” Special Agent Steve Schrank said.

He added that the operation was the result of a multi-month criminal investigation. It did not involve a substantial use of force and there were no significant physical injuries reported, he said.

“This was not an immigration operation where agents went into the premises, rounded up folks and put them on buses,” he said.

After carrying out a search warrant at the plant, agents encountered hundreds of individuals who were in the country illegally or working unlawfully, he said.

Videos on social media show agents lining workers up and telling them they have a warrant to search the facility. The agents can also be seen talking to some of the workers in the videos.

South Korea said it was dispatching diplomats to the site in response to the raid and that it had contacted the US embassy in Seoul to urge the US "to exercise extreme caution” when it came to Korean citizens’ rights.

“The economic activities of Korean investment companies and the rights and interests of Korean citizens must not be unfairly infringed upon during US law enforcement operations,” South Korea’s foreign ministry said in a statement.

The raid raises a possible tension between two of President Donald Trump’s top priorities – building up manufacturing within the US and cracking down on illegal immigration. It also could put stress on the country’s relationship with a key ally.

Trump has worked to bring in major investments from other countries while also levying tariffs he says will give manufacturers incentives to make goods in the US.

South Korean companies have promised to invest billions of dollars in key US industries in the coming years, partly as a way to avoid tariffs. Georgia’s governor, Republican Brian Kemp, had touted Hyundai's new electric vehicle operation as the biggest economic development project in the state’s history, employing 1,200 people.

But the president also campaigned on cracking down on illegal immigration, telling supporters that he believed migrants were stealing jobs from Americans.

Upon returning to office, he launched a massive effort across the country to round up people thought to be in the US illegally, hold them in detention facilities, and frequently deport them. While many of those caught in the sweeps have ties to Latin American countries, people of other nationalities have also been arrested. (BBC)