About 400 additional migrants also arrived in Tijuana on Tuesday by bus, a witness told Reuters.
"Our service members are performing duties along the Southwest Border in support of Customs & Border Protection and will continue to do so until otherwise directed by our senior leaders, to include the commander-in-chief", said Mike Kucharek, chief of integrated communications for U.S. Northern Command, which is overseeing the mission.
Hundreds of young men from one of the migrant caravans headed toward the United States arrived at a border fence that separates Tijuana, Mexico and San Diego, California on Monday; some of them began illegally entering the USA after climbing the fence.
More than 300 migrants had made it to Tijuana by Tuesday, according to the Post, as local officials said they're expecting larger numbers in the coming weeks.
Trump also followed through on his threat to issue a presidential proclamation barring migrants caught crossing into the USA illegally from being eligible to claim asylum in America.
That didn't deter arriving groups of Central Americans from going to a stretch of border fence in Tijuana to celebrate.
Saying many of them were from the LGBT community, one of the migrants said their travel was paid for by an anonymous organisation.
Members of the group would have traveled around 2,980 miles to make it from San Pedro Sula to Tijuana, with the caravan opting to take a longer route to the San Diego border rather than risk the shorter but more risky route to the nearest port of entry in the area of McAllen, Texas.
Watch some of the first migrants arrive in Tijuana above, via Global News.
For years, thousands of mainly Central American immigrants have embarked on long journeys through Central America and Mexico to reach the United States.
Mexico has offered refuge, asylum or work visas, and its government said Monday that 2,697 temporary visas had been issued to individuals and families to cover them during the 45-day application process for more permanent status.
Three northbound lanes will be closed at San Ysidro and another lane at Otay Mesa will also be closed to install "port hardening infrastructure equipment", the agency said in a statement. Some 533 migrants had requested a voluntary return to their countries, the government reported.
Migrant caravans heading to the USA became a campaign issue in US midterm elections.