Immigration enforcement authorities raided food processing plants across Mississippi on Wednesday, picking up 680 workers in what was being billed as the biggest single-day, one-state sweep in U.S. history, officials said.

The raids hit seven plants, owned by five companies, in six cities. Most of the workers arrested are Latino.

"While we are a nation of immigrants, more than that, first and foremost, we are a nation of laws," said U.S. Attorney Mike Hurst of the Southern District of Mississippi. "They have to come here legally or they shouldn’t come here at all."

Hurst also chastised businesses for using undocumented immigrants.

"To those who use illegal aliens for competitive advantage or to make a quick buck, we have something to say to you: If we find that you have violated federal criminal law, we're coming after you," he said.

Federal authorities would not say if the businesses who cooperated with the raids would be charged.

As of Thursday, 377 people remain in custody. Jere Miles, special agent in charge at Department of Homeland Security in New Orleans — which covers Mississippi — told reporters that 271 workers were released after being processed and receiving a date to appear in court, and 32 were released for humanitarian reasons.

Miles said 18 juveniles were picked up in the raids, including one as young a 14-years-old.

Local schools were made aware after the operations about how they can work with families to get in touch with ICE about detained parents, officials said. They cannot say if all parents have been released.

The long-planned raids unfolded as President Donald Trump traveled to El Paso, Texas, where 22 people were killed Saturday — allegedly by a man linked to an online screed about the "invasion" of Hispanic immigrants.

Trump has long railed against illegal immigration and began his presidential campaign by declaring that Mexican immigrants are "bringing drugs, they’re bringing crime" and that they're "rapists."

The acting director of Immigration and Customs Enforcement, Matthew Albence, said there was no connection between the timing of these raids and Trump's El Paso trip.

"This is a long-term operation that's been going on," Albence said. "Our enforcement operations are being done on a racially neutral basis. Investigations are based on evidence."

Albence told The Associated Press that the raids could be the largest such operation thus far in any single state.

In light of Wednesday's raids, the American Civil Liberties Union and the Southern Poverty Law Center both issued advisories urging anyone approached by ICE to remain silent, not open any doors without seeing a warrant, and demand to speak to a lawyer.

"It was a sad situation inside," said Domingo Candelaria, a legal resident and worker at Koch Foods Inc. in Morton, Mississippi, about 40 miles east of Jackson, where one of the raids took place.

The detained workers were expected to be processed at a hangar at the Mississippi National Guard in Flowood, near Jackson.