A migrant convoy of more than 600 people has crossed into Mexico and is heading north toward the southern U.S. border, prompting the Department of Homeland Security to issue a direct warning

The convoy started in San Pedro Sula, Honduras, on September 20 and grew as it traveled north, with migrants mainly from Honduras, Guatemala, Ecuador and Haiti.

DHS said "catch and release" has ended and warned:

"Anyone who tries to enter the US illegally will be caught, prosecuted and removed from the country."

The convoy comes just weeks before the US midterm elections, with immigration and border security remaining central issues in the campaign.