Caravan migrants, in the hundreds, reach Tijuana on the Mexico-U.S. border

Dozens of Central American migrants from about 600 travelling in a "caravan" through Mexico arrived at the border city of Tijuana late on Tuesday despite warnings it would be futile to try to cross to claim asylum in the United States.

By evening, two busloads of men, women and children arrived in Tijuana, a city that grazes southern California.

President Donald Trump, who launched his campaign in 2015 with talk of undesirables entering the U.S. from Mexico and then soon after pushed for a southern border wall, has ordered officials to repel them.

The arrivals spilled into the streets and gazed toward San Diego, visible at spots through a rusty barrier or across a pedestrian bridge, exhausted after their trek that began a month ago near Mexico's southern border with Guatemala.

Another four busloads were making their way north from Hermosillo, a city 695 kilometres south of the border, where the migrants had been stalled for days.

Claim their lives in danger

Many have fled their homes in Guatemala, El Salvador and Honduras because of what they described as lethal threats or political persecution; the countries have some of the highest per-capita homicide rates in the world. They have clung to the hope of receiving asylum in the United States, but their prospects dimmed after American authorities released statements on Monday saying they would be driven back.

"If members of the 'caravan' enter the country illegally, they will be referred for prosecution for illegal entry in accordance with existing law," Kirstjen Nielsen, secretary of Homeland Security, said in a statement. "For those seeking asylum, all individuals may be detained while their claims are adjudicated efficiently and expeditiously, and those found not to have a claim will be promptly removed from the United States."

Rodrigo Abeja, a coordinator from immigrant rights group Pueblo Sin Fronteras that has been organizing similar caravans for several years, said the caravan planned to regroup before making any decisions.

"They will wait for all those seeking asylum to be together," Abeja said. A third group, resigned to staying in Mexico, awaited processing for year-long visas by immigration authorities in Hermosillo.

Travelling as a group for safety, their numbers were down from a peak of about 1,500 people, dwindling under the twin pressures of waiting for transportation and attacks by Trump, who began lashing out at the caravan on Twitter in early April.

After Trump's comments, Mexican authorities stalled the caravan in a southern town and began handing out temporary visas that gave them legal status to travel to the border.

The caravan has been occurring for several years, and Department of Homeland Security reports indicate that the number of illegal border crossings into the U.S. is at a fraction of the rate that occurred in the 1990s a DHS report pegged the number at over 1.6 million in 2000 or even 2006, the last time the figure tracked over one million.

In 2017, the number of illegal crossings was estimated at over 310,000, the lowest total in 46 years.

While some on the left attribute this to the continuation of a historic trend, supporters of Trump point to his emphasis on the issue of illegal immigration and stepped-up U.S. Immigration and Customs Enforcement (ICE) interventions as discouraging