A former US Border Patrol deputy chief has defended the use of pepper spray on migrants at the US-Mexico border, saying it is “natural” and “you could actually put it on your nachos and eat it.”

Ron Colburn, who now leads the charity Border Patrol Foundation, told Fox News the substance was “a good way of deterring people without long-term harm.”

The comments came after US border agents used tear gas and pepper spray on crowds of migrants, some of them children, to deter them from entering the country illegally at the San Ysidro, California, port of entry near Tijuana, Mexico.

Mr Colburn said he felt the use of deterrents was “absolutely” necessary in order to protect Americans.

Mexico's Interior Ministry said it would immediately deport those who tried to "violently" come into the US at that entry point.

The local municipal government has declared a humanitarian crisis, as Juan Manuel Gastelum said his border city of 1.6m people was struggling to accommodate the influx of migrants.

Migrants enveloped in tear gas after heading toward US

More than three-dozen migrants were arrested for disturbing the peace and other charges stemming from the march and what followed over the weekend.

However, the situation further devolved into chaos as several migrants marched to the border to ask the US to expedite asylum applications for legal entry into the US.

US border agents have only been processing approximately 100 applications per day out of the nearly 5,000 people waiting at a sports complex in Tijuana.

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The Department of Homeland Security had also previously closed part of the San Ysidro port of entry, near the US city of San Diego.

These migrants are part of the so-called caravan of thousands who have travelled north through Mexico in an attempt to flee rampant gang violence and poverty in Guatemala, El Salvador, and Honduras.

Donald Trump consistently made reference to the caravan on the campaign trail and labelled them as “criminals,” “dangerous,” and accompanied by “unknown Middle Easterners”.

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He stationed nearly 5,000 US troops on the Texas border in order to stop any attempts to cross into the US as well.

Furious at the attempt to enter at San Ysidro, Mr Trump tweeted "Mexico should move the flag-waving Migrants, many of whom are stone cold criminals, back to their countries. Do it by plane, do it by bus, do it anyway you want, but they are NOT coming into the U.S.A. We will close the Border permanently if need be. Congress, fund the WALL!"

The administration continues to push for a nearly 2,000-mile border wall running along Texas, New Mexico, Arizona, and California, which Mr Trump repeatedly promised Mexico would fund.