A stretch of rural southeast Georgia, just outside Savannah, has been transforming rapidly in recent years, as a plan to create a massive manufacturing hub capable of producing nearly half a million vehicles per year has come to fruition.

The complex has embodied the ambitions of South Korean automakers wanting to compete in the U.S. market. It has also been a crowning achievement in a long campaign by Georgia officials to draw Korean investment. Until recently, crews had been busy building the latest piece of that effort, a plant making batteries for electric vehicles.

But that vision has become clouded by uncertainty after federal immigration authorities raided the plant on Thursday, halting construction. Nearly 500 workers — many of them South Korean citizens — were arrested.

The raids, described by government officials as the largest Homeland Security enforcement operation at a single site, have exposed growing strain that reaches from Seoul to Washington and even a small, unincorporated community like Ellabell, Ga., where the plant is being built.

South Korea, an enthusiastic trading partner, expressed frustration with the United States. Within the Trump administration, the arrests have revealed competing interests, as a push by the president to expand U.S. manufacturing has collided with his aggressive crackdown on immigration. And in Ellabel and the surrounding area, the raids have revealed conflicting emotions about how quickly the region is changing, and over who is filling the jobs that are being created.

Law enforcement officials said the raid on Thursday followed a monthslong investigation into suspicions of unlawful employment practices at the HL-GA Battery Company plant, a joint venture of LG Energy Solution and Hyundai Motor Group. Margaret E. Heap, the U.S. attorney for southern Georgia, said in a statement that the operation had been intended to “prevent employers from gaining an unfair advantage by hiring unauthorized workers.”