US Customs and Border Patrol (CBP) says the “dramatic rise” in migrants from African countries arriving in the area is a “humanitarian crisis”.
More than 500 African migrants have arrived at Del Rio border patrol sector in the past week, since 30 May.
Most of these people are families that have travelled from Angola, Cameroon and the Republic of Congo, CBP said.
Last week, on 30 May, one large group of 116 people who had all originally travelled from African countries arrived at the southern border.
In a statement, Del Rio Sector’s chief patrol agent Raul L Ortiz said that language barriers and cultural differences were also placing “additional burdens on [border patrol] processing stations”.
Many of the migrants have also travelled on to San Antonio in Texas, some 240 km (150 miles) from Del Rio.
A spokeswoman for San Antonio’s city government told BBC News that they were “operating a resource centre for those travelling” and have “partnered up with local charities” to provide people with necessities such as food and shelter.
Local news reporter Jaleesa Irizarry also tweeted that the city was “in desperate need for French-speaking volunteers”, and that local centres expected up to 300 more migrants to arrive in the next few days.