President Donald Trump has made this caravan a symbol of a porous border and lax immigration laws. He has used it as justification to deploy National Guard troops, and his comments about it have further strained US relations with Mexico.
And yet, many of these migrants are likely to eventually enter the United States, at least temporarily, as the law allows, so that their claims of fear and persecution in their home countries can be heard before a court.
US Customs and Border Protection Commissioner Kevin McAleenan warned in a statement that the San Ysidro point of entry had "reached capacity" and that the migrants "may need to wait in Mexico as CBP officers work to process those already within our facilities."
At a last gathering here before walking to the port of entry, caravan organisers and migrant advocates called on the Trump Administration to treat these people humanely and according to the law. Those who weren't processed by US authorities would wait and could use the time in Tijuana to gather evidence to support their asylum claims, said Irineo Mujica, the director of Pueblo Sin Fronteras, a migrant rights group that organised the caravan.
"We hope the United States will take them in," Mujica said. "If not, we've already waited through a month of torture with Donald Trump. I think we can wait a couple more."
In past years, such caravans have served to call attention to the plight of migrants on a dangerous journey, but they often travelled in obscurity. This year, conservative media in the United States seized on the caravan as a sign of out-of-control immigration, and Trump fanned the flames in a series of tweets.
As members of the group reached the border, US officials suggested that they should stay in Mexico and warned them - and the activists helping them - against making false immigration claims, saying that they would be prosecuted if they did.
"To anyone that is associated with this caravan, Think Before You Act," Rodney Scott, chief patrol agent in San Diego for the US Border Patrol, said in a statement. "If anyone has encouraged you to illegally enter the United States, or make any false statements to US government officials, they are giving you bad advice and they are placing you and your family at risk."
The caravan started out with more than 1500 people, but the numbers dwindled to about 200 as the group made its way north by foot, bus and train. Some have dispersed, and others chose to stay in Mexico.
About 300 people remained in the northern Mexican city of Hermosillo to apply for humanitarian visas, said Mujica, the caravan organiser. But he said the Mexican Government has yet to issue the visas.
"We are asking the Mexican Government to come through with their promises. They promised close to 1000 visas, and of those, not a single one has been issued," Mujica said.
The group gathered alongside the beach in Tijuana at a park where the border fence juts into the Pacific Ocean.
"I'm feeling happy, but nervous at the same time. What if they don't give us asylum and send us back to our country?" said Reina Carolina García Marin, 16, who said she was fleeing San Pedro Sula, Honduras, after a gang member raped her high school friend - and then informed her that she was next on the gang's list.
Some migrants hesitated on the border as they learned about conditions in U.S. detention centers. The approximately 40 lawyers and legal assistants who facilitated group workshops gave them individual advice about their asylum cases, while informing them that they probably would be held initially in a frigid room called the hielera - Spanish for icebox - and that adults could be detained for several months, or even years. Families were likely to be separated into different detention centers. Single men can generally expect to spend longer in detention.
Miguel Angel Lopez, 29, who had fled from Olocuitla, El Salvador, because gang members sought to recruit him, was discouraged by his prospects.
"It seems impossible to get asylum, because you could have to wait for up to a year, and to pay up to US$20,000," he said.
US law generally allows foreigners to apply for asylum, but the vast majority of Central Americans who apply are not approved. Migrants who pass the initial "credible fear" screening often get assigned a date in immigration court and then are released after a few days in custody. US officials say many migrants skip their court dates and try to live illegally in the United States.
Trump has vowed to end what he calls President Barack Obama's "catch and release" immigration policies, but recent figures show that the Trump Administration has released about 100,000 people at the US-Mexico border - many with ankle monitors to track them until their court dates.
"There's a luck-of-the-draw aspect based on what jurisdiction they end up in, and what jurisdiction they end up in is basically a lottery based on what beds are available," said Alexandra Bachan, an immigration lawyer based in Oakland.
The group stalled outside the port of entry as they debated whether to enter together or go in small groups. Ruben Figueroa, a representative from Mexico's immigration agency, suggested a small group, of about 20 people, should go first "to see the response of the US authorities."
Maria Magdalena Iraeta Martínez, 47, of El Salvador, said she was planning to "cross with my kids to a place where I can finally be free, without threats."
Five years ago, Martínez said, her family had been encircled in their home by armed members of the MS-13 gang. The gang members had attempted to recruit her son, William Rafael Carranza Martínez, now 25, but he had refused to join. Armed men entered the house early in the morning, escorted all of the extended family outside and threw them to the ground at gunpoint, she said.
The family fled to Guatemala and lived for several years in southern Mexico but continued to receive gang threats.
At the front of the caravan, Carranza pushed his sister's wheelchair up the ramp leading to the port of entry. His mother, Iraeta Martínez, followed behind, crying.
"I ask God and the government to give me asylum," she said.
