U.S. Customs and Border Protection says a “dramatic rise” in the number of African migrants crossing the U.S. border is contributing to a “humanitarian crisis,” according to the BBC.

More than 500 migrants from countries such as Cameroon, the Democratic Republic of the Congo, and Angola have arrived at the Del Rio border station in Texas since May 30, including a group of 116 people, says the BBC.

Customs officials say the influx of migrants is overwhelming. “When we have 4,000 people in custody, we consider it high,” Customs and Border Patrol’s commissioner John Sanders told a press conference, according to the BBC. “If there’s 6,000 people in custody, we considered it a crisis. Right now, we have nearly 19,000 people in custody. So it’s just off the charts.”

Read More: Border Patrol Says Group of 1,036 Migrants Is the Largest the Agency Has Ever Encountered

Some have continued on to San Antonio. A local news reporter, Jaleesa Irizarry, said on Twitter that the city was in need of French-speaking volunteers. She also said that more migrants are expected to arrive over the next few days.

A San Antonio government spokeswoman told the BBC that they are working to provide food and shelter through a resource center and partnerships with local charities.

It is unclear what path the migrants are taking to get to the U.S.-Mexico border, but some migrants from African countries have reported traveling from Africa to Brazil before heading north to the U.S, according to the BBC.

Write to Amy Gunia at amy.gunia@time.com.