Migrants crossing the Tijuana River as they approach the US border.

The incident took place near the "El Chaparral" pedestrian border crossing into the United States. Blocked by Mexican police at the approach to the crossing, the marchers turned away and headed toward a vehicle border crossing and another pedestrian crossing a few minutes away. Mexican federal police had blocked the road where cars usually enter Mexico from the US with a large metal gate, and it seemed unlikely the migrants could have passed through it, but Mexican police quickly cordoned off the area, making access impossible.

Altogether, the confrontation lasted nearly two hours before the migrants appeared to withdraw and return to the stadium where they have been camping for days.

More than an hour after the first tear gas use, Border Patrol agents fired tear gas at another group as it was crossing the Tijuana River, sending the crowd that had gathered there fleeing.

The Mexican official, who requested anonymity because they weren't allowed to speak to the press, said Mexican authorities were trying to identify people who tried to "violently" cross into the US in order to deport them.

At least one person crossed through the barrier and was detained by a US border agent, according to a witness. A Mexican government official said 30 migrants breached the US border and were apprehended by United States authorities. US officials did not respond immediately to a request for confirmation.

With helicopters circling overhead, US border authorities fired tear gas and, according to witnesses, rubber bullets as some of the marchers approached the United States at a metal fence where train tracks run through.

TIJUANA, Mexico — US authorities on Sunday temporarily shut the San Ysidro Port of Entry, one of the world's busiest border crossings, after hundreds of migrants from Central America evaded a phalanx of Mexican police, crossed a small river, and marched down a side street in front of a pedestrian crossing.

People went around the police blocked overpass through a side street and crossed the river for the border crossing. The group is now congregating to the side of the port of entry. https://t.co/bRUJRGI7OD

It was the first confrontation between the caravan and US authorities, and it seemed certain to heighten tensions in this already tense border metropolis. Only a day earlier, US troops had conducted a training exercise at the San Ysidro crossing, according to photos posted on a US military Facebook page. As if to emphasize US readiness, the photos were posted within minutes of Sunday's confrontation.

Little was known about what role, if any, US active-duty troops dispatched to the border to support US Customs and Border Protection played in the confrontation, however. A spokesman for US Northern Command, which oversees troops in the US, stressed that the active-duty troops won't be conducting any law enforcement functions.

However, the spokesperson said military engineers “moved barricades and military police as part of the additional personnel presence” at the San Ysidro port of entry at the request of CBP on Sunday.

The marchers left Estadio Caliente, the Tijuana stadium where many have been living for days, at about 10 am Pacific time and walked toward the border, carrying signs that said "Donald Trump, Christ loves you" while others held US, Mexican, and Honduran flags painted onto pieces of cloth.

At one point, Mexican police urged the marchers to turn back, saying they were risking their opportunity to ever enter the United States.

“It was all really confusing, we were all just following the person in front of us,” said Alex Almendorez, 32, of Honduras.

The first tear gas was fired at about 12:15. At about 1 p.m. the group started to leave the train tracks and walked back in the direction of the outdoor stadium.



Eduardo Avila called his wife after leaving the train tracks, concerned that she had seen the live television coverage and was worried about him. She hadn’t seen the coverage but told him she was glad he was okay.

“Some people tried to cross and that’s when they threw the gas,” Avila told BuzzFeed News.



Cynthia Fajardo, 18, was also at the train tracks when the group was teargassed and said there were a lot of kids in the area. The Honduran national had hoped the group would be able to cross on Sunday.

“All we can do now is wait and see if Trump will let us enter,” Fajardo told BuzzFeed News.

Shortly before 2 p.m., the Border Patrol fired at a group that was crossing the Tijuana River. Shortly thereafter, the group started walking back to the outdoor stadium.

The caravan in Tijuana has grown to 5,157 people, according to local government officials. That number is expected to grow as other groups of migrants arrive.

Julio Ulloa, 29, helped paint some of the posters and signs for the march. He said the members of the caravan marched to the border walkway in the hopes of asking President Trump for some type of permission to enter the United States.

"Trump says he won't open the door but God has the last word," Ulloa told BuzzFeed News.

Many people inside the sports complex have grown frustrated with the long delay to apply for asylum, Ulloa said. Some have slept within view of the border wall and the United States. They were cold, and there wasn't enough food and water for everybody, he added.

The Honduran native said the caravan had been well received through its entire trip through Mexico, but they felt unwelcome in Tijuana, pointing to an anti-immigrant march that took place recently and statements from the local government about limited resources.

"People are frustrated," Ulloa said. "We barely fit and there are more people coming."

Zabludovsky reported from Mexico City. Vera Bergengruen contributed reporting to this story from Miami.