Yahoo TV

STORY: These scenes of thousands of migrants gathered at the U.S.-Mexico border are reminiscent of the influx the country saw before U.S. President Joe Biden in May rolled out a new policy to deter illegal crossings.

Within a month, those tough measures such as deporting migrants and banning re-entry for five years drove the border-crossing rate down some 70%.

But four months on, and the early deterrent effect appears to be wearing off.

Record numbers of migrants, in the thousands, have crossed into the United States in recent days,

with many more still arriving by bus and cargo trains to Mexican border towns.

The surge could represent a looming political challenge for Biden heading into election season.

Enrique Lucero is Tijuana's director of migrant affairs.

"The big problem we see is that it could become a humanitarian crisis. Irregular border crossings are being encouraged, generating organised crime and human trafficking. These are the risks we see if decisions are not taken promptly."

Experts say the U.S. lacks the capacity to detain and process migrants at the border often making it impossible for the administration to carry out the harsh penalties it announced in May.

And as a result, some asylum seekers who cross illegally are being released into the U.S. with a future court date, rather than being deported.

Their success stories are repeated back to migrants still en route.

This Venezuelan migrant, still on the Mexican side of the border, says he heard rumours about people being let into the U.S. after turning themselves into border agents.

He's determined to continue on his journey.

The U.S. Customs and Border Protection meanwhile has told Reuters that it was "safely and efficiently" processing migrants and would impose consequences, including deportation, on migrants without a legal basis to stay in the country.