The Department of Homeland Security has put out a call for employees to volunteer at the southern border, as officials say they are tackling "large numbers" of migrants -- and amid ongoing concerns about a coming surge in the spring and summer months.

The Wednesday email by Deputy Secretary John Tien, and seen by Fox News, requests volunteers for the DHS Volunteer Force, more than a year after the volunteer force was activated ahead of last year's migrant surge. The force has also been used to help with the Afghan evacuee resettlement operation last year, as well as during the 2019 border crisis. The email says more than 1,400 employees have volunteered.

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"Once again, we need to tap into our Department’s greatest resource: the skills of our talented and diverse workforce. Today, I am asking you to consider stepping forward to support the DHS Volunteer Force," it says.

"[Customs and Border Protection] continues to encounter large numbers of individuals at the Southwest Border," the email says. "We are seeking your help to support our CBP frontline workforce."

The email says that the department needs volunteers in two areas -- general support and data entry (with Spanish language skills.)

Aug 12, 2021: Alejandro Mayorkas, secretary of the U.S. Department of Homeland Security, speaks during a new conference in Brownsville, Texas, U.S. (Veronica G. Cardenas/Bloomberg via Getty Images)

Aug 12, 2021: Alejandro Mayorkas, secretary of the U.S. Department of Homeland Security, speaks during a new conference in Brownsville, Texas, U.S. (Veronica G. Cardenas/Bloomberg via Getty Images) (Veronica G. Cardenas/Bloomberg via Getty Images)

A Border Patrol source told Fox News that there is a "frantic sense of urgency" as officials work to get processing capabilities in place at both the southern and northern borders. 

"We are limiting agents in the field just to have more processing," the source said.

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The email was first reported by Axios, which also reported that officials are preparing for a surge of more than 170,000 migrants if the administration ends Title 42 -- a public health order put in place by the Trump administration at the start of the COVID-19 pandemic which allows for the rapid expulsion of migrants at the border.

Activists and top Democrats have pushed for the Biden administration to end the Centers for Disease Control (CDC) order, but with February’s migrant encounters up more than 60% over last year, it has raised fears of a migrant surge in the spring and summer that could outpace 2021’s mammoth surge. More than half of the 164,973 migrants encountered in February were expelled under Title 42.

Part of the preparations reportedly include a new Southwest Border Coordination Center, which Axios describes as a "war room" to coordinate the response to the brewing crisis that officials are fearing could be a "mass migration event."

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The response could include a surge of additional personnel, aircraft from the U.S. Marshals Service to transport migrants to other parts of the border, buses from the Bureau of Prisons and new soft-sided facilities to hold thousands of migrants, the outlet reported.

In response to a query on the Axios report, White House spokesperson Vedant Patel told Fox News: "Of course the administration is doing our due diligence to prepare for potential changes at the border. That is good government in action." 

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"As always is the case this Administration is working every day to restore order, fairness, and humanity to our immigration system and bring it into the 21st century," he said.

Fox News’ Kristina Biddle contributed to this report.