The San Ysidro port of entry, among the largest border crossings between San Diego and Tijuana, was shut down by U.S. Customs and Border Protection agents Sunday after hundreds of caravan migrants appeared to have attempted to breach a U.S.-Mexico border fence.

CBP officials closed traffic roads moving in both directors and pedestrian walkways at the port of entry. An Associated Press reporter said tear gas was fired at the migrants from inside the U.S.

"Warning: Due to the current situation, the San Ysidro Port of Entry is now closed." U.S. border officials shut down the port of entry between San Diego and Tijuana as thousands of Central American migrants wait in Mexico to apply for asylum in the U.S. https://t.co/tYqgGQlc4L pic.twitter.com/566gPUMneN — ABC News (@ABC) November 25, 2018

The freeway just north of the #SanYsidro Port of Entry is shut down pic.twitter.com/RdvX0msJYm — Ramon Galindo (@RamonGalindoNBC) November 25, 2018

Pueblo Sin Fronteras, the group organizing the caravan, told Fox News that migrants were preparing to breach the Southern California border crossing on Sunday.

Footage of migrants rushing the port of entry is making the rounds on social media.

Hundreds try to storm the border. Expect significant US response #tijuana pic.twitter.com/0T50XUnXtY — emma murphy (@emmamurphyitv) November 25, 2018

Warning raw video may have cuss words pic.twitter.com/ORrA8rMXoO — WendyFry (@WendyFry_) November 25, 2018

#BREAKING: Lanes and pedestrian crossings close at San Ysidro Port of Entry amid border marches. https://t.co/11cUSvrzrp pic.twitter.com/N42EADvaEx — #NBC7 San Diego (@nbcsandiego) November 25, 2018

Here’s moment right before shot bang. You can see some rocks being thrown. pic.twitter.com/p0M9p7Rx4G — WendyFry (@WendyFry_) November 25, 2018

U.S.-Mexico border near Tijuana closed as migrants attempt to breach fence: “Some of these migrants attempted to breach legacy fence infrastructure…and sought to harm CBP personnel by throwing projectiles at them,” DHS Sec. Nielsen said in a statement. https://t.co/YP5cIFX5KZ pic.twitter.com/U0voEg1yAs — ABC News (@ABC) November 25, 2018

In one video shared by ITV reporter Emma Murphy, migrants are heard shouting “yes we can” as they rush the entry point.

Some pushing right to fence shouting “yes we can”. pic.twitter.com/m03bNX9LIk — emma murphy (@emmamurphyitv) November 25, 2018

U.S. Border Patrol helicopters flew overhead, while U.S. agents held vigil on foot beyond the wire fence in California.

Military helicopters are flying over the border as @CBPSanDiego agents in riot gear block the roadway pic.twitter.com/OCG0lQfexo — Ramon Galindo (@RamonGalindoNBC) November 25, 2018

More than 5,000 migrants have been camped in and around a sports complex in Tijuana after making their way through Mexico in recent weeks via caravan. Many hope to apply for asylum in the U.S., but agents at the San Ysidro entry point are processing fewer than 100 asylum petitions a day.

A second line of Mexican police carrying plastic riot shields stood guard outside a Mexican customs and immigration plaza, where the migrants were headed.

That line of police installed tall steel panels behind them outside the Chaparral crossing on the Mexican side of the border, which completely blocked incoming traffic lanes to Mexico.

Hours after the attempted breach, Homeland Security Secretary Kirstjen Nielsen issued the following statement: “After being prevented from entering the Port of Entry, some of these migrants attempted to breach legacy fence infrastructure along the border and sought to harm CBP personnel by throwing projectiles at them. 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,” the statement continued. “We will also seek to prosecute to the fullest extent of the law anyone who destroys federal property, endangers our frontline operators, or violates our nation’s sovereignty.”

DHS Sec. Nielsen issues statement on San Ysidro Port of Entry closure: “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.” https://t.co/qityKL6n9A pic.twitter.com/4eDIgMbNIr — ABC News (@ABC) November 25, 2018

Tijuana Mayor Juan Manuel Gastlum 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.

The Associated Press contributed to this report.