As many as 10,000 migrants are believed to be traveling with caravans from Central America to the United States with the hopes of entering the country, senior administration officials said Monday.

Between 8,500 and 10,500 people are making their way from Northern Triangle countries El Salvador, Guatemala, and Honduras to America’s southern border. About 6,000 have already made it to Tijuana, a city of 1.7 million residents that sits just over the border from San Diego, Calif.