The first caravan of Central and South American migrants seeking asylum in the U.S. has arrived at the border city of Tijuana.
The group of 400 people broke away from the larger caravan of 5,000 in Mexico City.
Larger groups are expected to reach the border in the coming days.
U.S. Defense Secretary James Mattis was due to visit the border on Wednesday, his first trip since thousands of American troops were deployed.
U.S. authorities also closed down several lanes of traffic at two border crossings from Tijuana to California on Tuesday so that soldiers can install barbed wire fencing and barricades.
President Trump signed a decree last Friday that effectively suspended the granting of asylum for those who cross the border illegally, a move that could drastically slow claims at gates of entry.
