Media playback is unsupported on your device Media caption The raids were carried out by hundreds of ICE agents

US immigration officials have arrested almost 700 people after a series of raids in the state of Mississippi.

The co-ordinated operations targeted workers at seven agricultural processing plants who allegedly did not have proper documentation.

Videos and photos showed agents arriving in buses to question and arrest the people.

Some children were taken to a local gym after they came home to find their parents gone.

Immigration and Customs Enforcement (ICE) said "approximately 680 removable aliens" had been detained.

US President Donald Trump announced an immigration crackdown in June, saying "millions of illegal aliens who [had] found their way into the US" would be removed.

The raids took place just hours before Mr Trump arrived in the majority Latino city of El Paso to mark a mass shooting which left 22 people dead.

What happened at the plants?

About 600 ICE agents arrived at the chicken processing plants, owned by five different companies, in the towns of Bay Springs, Canton, Carthage, Morton, Pelahatchie and Sebastopol.

The agency's acting director, Matthew Albence, told the Associated Press news agency it was one of the largest enforcement operations against undocumented immigrants.

Friends and family looked on as officers surrounded plants and began to arrest the workers.

Skip Twitter post by @ashtonpittman At a Mississippi school, the children and family members of immigrants plucked out of their workplaces by federal agents in today’s historic #ICEraids weep, unsure when or if they’ll see their loved ones again. Their back to school week. Shared with permission from Miriam Sanchez pic.twitter.com/0vr3CEWPTj — Ashton Pittman (@ashtonpittman) August 7, 2019 Report

One video posted on Facebook showed people gathered outside a Koch Foods plant in Morton.

A child - daughter of one of the detained women - can be heard weeping uncontrollably as people are loaded onto a bus.

"Her mum is in there," a woman tells a police officer. "Her mum is her only legal guardian."

The crying girl asks the officer, "Please, can I just see my mother, please." The child was eventually allowed to see her mother before she was taken away.

When the officer returned the girl to the women helping her, he said her mother would be released the same afternoon.

"I'm going to tell you something, she's not going to be deported because she has a US citizen child," the officer said.

"Everything's going to be fine, alright, don't you worry about it, your mom's not going to be deported, I promise you," he told the girl.

As the buses drove off with the detainees, those gathered outside reportedly chanted, "Let them go!" and waved goodbye.

According to the Washington Post, the girl's mother was not released as of Wednesday night.

Mr Albence said the children would be sent to live with relatives or with other families, according to AFP news agency.

Some were taken to a local gym by neighbours after coming home from school to find their parents gone.

Skip Twitter post by @AlexLoveWJTV Children of those arrested in Wednesday’s #ICE raids near Forest, MS. are being put up in a local gym tonight by neighbors/strangers. Many are left scared & crying after coming home from school & being locked out without their parents. Donated food & drinks are being provided. pic.twitter.com/d2juMdK1Vj — Alex Love (@AlexLoveWJTV) August 8, 2019 Report

Scott County schools superintendent Tony McGee told the Clarion Ledger newspaper that one child had started kindergarten on Tuesday, only to have their parent arrested on Wednesday.

Mr McGee said at least six families had a parent detained in the raids, with children ranging in age from kindergarten to high school.

"We'll worry about the school part of it after we get all this sorted out," he added. "You can't expect a child to stay focused on the schoolwork when he's trying to focus on where Mom and Dad are."

Those detained were taken to a Mississippi National Guard hangar for questioning.

According to a statement released by ICE, some may be temporarily released after "consideration of their criminality and prior immigration history".

ICE has not given details about the nationality of those detained, but the Mexican government has reportedly sent consular staff to the area to help any of their nationals who may be involved.

What's been the reaction?

Jackson Mayor Chokwe Antar Lumumba condemned the raids as "dehumanising and ineffective".

But Mike Hurst, US Attorney for the Southern District of Mississippi, said ICE agents were executing warrants to arrest the "illegal aliens".

"They have to follow our laws, they have to abide by our rules, they have to come here legally or they shouldn't come here at all," he told a press conference.

Some Trump supporters on Twitter also backed the agency, saying the law must be enforced.

Skip Twitter post by @CarmineSabia Im sorry for the kids whose parents were caught in the #ICERaids. It is a tough lesson for these kids on obeying rules and laws. There are consequences. I have sympathy for the kids but parents of Americans are arrested daily and the kids cry. We still enforce the law. — Carmine Sabia (@CarmineSabia) August 8, 2019 Report

Democratic presidential hopeful Kamala Harris said in a tweet: "These ICE raids are designed to tear families apart, spread fear, and terrorize communities. These children went to daycare and are now returning home without their parents because Trump wants to play politics with their lives."

Fellow 2020 contender Cory Booker echoed the same sentiment.

"The moral vandalism of this administration has no end - how is traumatizing these kids, abandoning them, making anyone any safer?"