"The situation on our southern border is grim," the secretary wrote, adding that customs and border guards, as well as immigration and customs enforcement, are "not equipped" to handle the current migration spike.
The secretary's request, which was sent to those responsible for the agency, included the need for volunteers to help with transport, food distribution, medical assessment and "hospital monitoring". The department consists of 14 components, including the Federal Emergency Management Agency, the Transportation Security Administration and the Coast Guard.
Nielsen also called for lawyers to volunteer as part of a 12-month rotation to prosecute immigration and support cases.
And she asked for help from doctors and other healthcare professionals to assess and evaluate detained migrants.
Nielsen issued a statement Friday in which she said she had asked for volunteers to help within the Department of Homeland Security and that she also called for "more help from inter-agency partners."