Hundreds of Transportation Security Administration officials are being deployed to the U.S.-Mexico border to assist in dealing with migrants arriving at the southern border.

The TSA workers will be temporarily helping with immigration duties, and, according to an internal email obtained by CNN, the assignment will create 'some risk' of depleted resources in aviation security during a 'very busy summer' travel season.

Those deployed will including air marshals, who fly in civilian clothes on commercial flights to prevent terror attacks.

'There is now immediate need for more help from TSA at the SW border,' Gary Renfrow, a senior TSA official, wrote in the email to the agency's regional management.

'TSA has committed to support with 400 people from Security Ops,' he said, adding that they will be deployed in waves 'similar to support for past hurricanes.'

President Donald Trump's administration is deploying hundreds of Transportation Security Administration officers to the southern border to assist with immigration duties

Although the deployments will not initially include uniformed TSA screeners, it will include law enforcement officials and air marshals, which the administration says would likely produce 'some risk' in airport security during the 'very busy summer' travel season.

The TSA assignment comes as illegal border crossings spike and apprehensions hit a 10-year high

In addition, TSA will initially send 42 law enforcement officials to the border from six different cities, and that number will eventually grow to 175, according to two sources.

Other parts of TSA will be asked to contribute around 10 per cent of its workforce, but the efforts will not include unformed airport screeners, Renfrow said in the email.

The law enforcement officials will be designated as immigration officers following legal training, according to a source familiar with the plans, and the individuals deployed will assist Customs and Border Protection employees with their work.

Before she was ousted as Department of Homeland Security secretary last month, Kirstjen Nielsen asked volunteers from DHS, including those working for TSA, 'to assist CBP and ICE [Immigration and Customs Enforcement] in responding to the emergency at the southern border.'

Acting Secretary of Homeland Security Kevin McAleenan, who used to run CPB, took over for Nielsen, and TSA Administrator David Pekoske was selected as his deputy at DHS.

Before her ousting last month then-DHS Secretary Kirstjen Nielsen asked volunteers from DHS, including TSA employees, 'to assist... in responding to the emergency at the southern border'

The acting DHS secretary, Kevin McAleenan (pictured), used to run CPB, and TSA Administrator David Pekoske was selected as his deputy

An internal TSA email noted Pekoske's (pictured) dual role. The border effort is 'a high priority for DHS, and our Administrator,' the email reads

The recent email notes Pekoske's dual role and describes the border effort as 'a high priority for DHS, and our Administrator.'

The TSA plans come as illegal border crossing apprehensions hit a 10-year-high.

Acting defense secretary Patrick Shanahan said recently that there are 4,300 active duty military and National Guard troops already assisting at the border.

Customs and Border Protection also moved 750 of its officers last month from other assignments to assists with Border Patrol.

'TSA, like all DHS components, is supporting the DHS effort to address the humanitarian and security crisis at the southwest border. TSA is in the process of soliciting volunteers to support this effort while minimizing operational impact,' TSA spokeswoman Jenny Burke said in a statement.

The assignment will result in a decrease in about 8 per cent of federal air marshal operations and 20 per cent in Visible Intermodal Prevention and Response patrol operations.

In February, following a budget fight with Congress over border wall funding, President Donald Trump declared a humanitarian crisis at the border, citing illegal crossings and the rise in crime, including human trafficking and drug smuggling.