According to Trump, Border Patrol had to utilize tear gas because hundreds of caravan riders were becoming violent and agents' lives were at risk. At least one man was wounded.
"Entering our country illegally, particularly over our walls, is not only risky, but also very foolish", said Rodney Scott, San Diego's Chief Border Patrol Agent, according to KFMB.
Geoffrey Hoffman, a professor and director of the University of Houston Law Center Immigration Clinic, which represents migrants applying for asylum, said the government would use it to push the argument that the migrants should remain in Mexico.
The US Government has defended its response to use tear gas after left-wing critics in the country said it was an over-the-top response.
US President Donald Trump recently commented on the tear gas deployment, telling reporters on Monday that migrants forced the hand of the CBP.
For weeks before the 6 November congressional elections, Mr Trump raised the alarm about the migrant caravans and ordered some 5,800 USA troops to the border to support border patrol agents.
American authorities also shut down the nation's busiest border crossing at San Ysidro for several hours at the end of the Thanksgiving weekend. He is anticipating that thousands of more migrants will arrive soon.
"Mexico should move the flag waving migrants, many of whom are stone cold criminals, back to their countries". More police carrying plastic riot shields were on the other side, but migrants walked along the river to an area where only an earthen levee and concertina wire separated them from U.S. Border Patrol agents. "Congress, fund the WALL!"
With the caravan as a backdrop, Trump has used national security powers to circumvent longstanding immigration law to deny asylum to anyone caught crossing the border illegally.
US asks allies to avoid Huawei's equipment
Apparently, the latest warnings come due to US concerns over the use of equipment from China in countries with USA military bases. The US has slapped tariffs on billions of dollars of Chinese imports, drawing swift retaliation from the Chinese government.
Rosie O'Donnell said the border clash was "pure horror" and called for the removal of President Trump.
Although Mexican police were stationed nearby, they were outnumbered and overwhelmed by the unexpected rush.
Several hundred made it over the first barrier, with video clips posted on Twitter showing crowds of people dashing across a shallow concrete riverbed toward the United States.
"Star Trek" star George Takei wrote: "Make no mistake: Trump is testing whether he can get away with things like firing tear gas at young children".
The migrants covered their faces to protect themselves from the acrid gas.
US Homeland Security Secretary Kirstjen Nielsen accused the migrants of seeking to harm US border patrol personnel "by throwing projectiles at them".
Trump previously indicated that the "whole" of the United States southern border may close, should the Mexican government not be able to get control of the migrant caravan situation.
But on Monday, the incident had left many migrants sullen, wondering whether the unrest had spoiled whatever possibilities they might have had for making asylum cases.
"If it was a protest, it was a really stupid way to go about it because there were individuals who started throwing rocks and other projectiles", Shawn Moran, vice president of the National Border Patrol Council, told the paper of the November 24, 2013, incident. He said CBP does not have rubber bullets in its inventory on the border.