U.S. Customs and Border Protection closed the San Ysidro border crossing outside of San Diego Sunday, as hundreds of migrants trying to enter the U.S. - many of whom are seeking asylum - gathered at the border and demanded entry.
The gas reached hundreds of migrants protesting near the border after some of them attempted to get through the fencing and wire separating the two countries.
Children screamed and coughed in the mayhem of the tear gas.
More demonstrations were planned on Sunday at San Ysidro, the busiest land port of entry in the Western Hemisphere, according to the US General Services Administration.
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Some of them even started throwing rocks at agents, and US agents reportedly responded by throwing tear gas into the crowd. The crowds were made up of men, women and children, he said.
Earlier Sunday, the group of several hundred migrants pushed past a blockade of Mexican police who were standing guard near the global border crossing. "We must choose to be better than this, and @realDonaldTrump expected nothing less when he deployed thousands of troops to the border with the order to shoot to kill", Amnesty said on Twitter. "The vast majority of people we're dealing with are adult males".
Mexico's Interior Ministry said Sunday it would immediately deport those who tried to "violently" enter the USA from Tijuana.
"As I have continually stated, DHS will not tolerate this type of lawlessness and will not hesitate to shut down ports of entry for security and public safety reasons", Nielsen said. "We will also seek to prosecute to the fullest extent of the law anyone who destroys federal property, endangers our front-line operators, or violates our nation's sovereignty".
A Facebook page set up for the San Diego "March of Solidarity with the Refugee Caravan" suggests that more than 500 demonstrators attended the event, which was organized by several groups, including the Migrant and Refugee Solidarity Coalition, People Over Profits San Diego and Unión del Barrio.
The situation devolved after the group began a peaceful march to appeal for the U.S.to speed processing of asylum claims for Central American migrants marooned in Tijuana.
Tijuana Mayor Juan Manuel Gastelum on Friday declared a humanitarian crisis in his border city of 1.6 million, which he says is struggling to accommodate the crush of migrants.
"Would be very SMART if Mexico would stop the Caravans long before they get to our Southern Border", Trump wrote on Twitter on Sunday.
Trump has repeatedly warned that the large group of migrants moving through Mexico toward the U.S. included criminals and possibly terrorists, while providing no evidence to support that. He called on the Mexican government - specifically, President Enrique Peña Nieto and his secretary of domestic affairs - to provide assistance.
The Tijuana government said officers arrested 39 people.