U.S. border officials on Monday shut down all vehicular traffic flowing north from Mexico into California at the country's busiest border crossing and diverted staff to help bulk up the infrastructure and security there, in anticipation of the arrival of thousands of migrants traveling in caravans from Central America.

The San Ysidro port of entry, which processes 20,000 pedestrians and 70,000 vehicles moving from Tijuana to San Diego each day, closed all passenger and commercial lanes and one of its two pedestrian crossings.

The port's 26 passenger lanes and 22 pedestrian lanes see more traffic than any in the entire Western Hemisphere.

[Read more: Migrants from caravan begin climbing border fence in Tijuana]

"U.S. Customs and Border Protection officials have temporarily suspended vehicle processing for northbound travelers at the San Ysidro port of entry Monday morning to position additional port hardening materials," CBP, the federal agency that oversees all port activity, said in a statement issued Monday.

An unspecified number of "temporary impediment measures," or objects meant to block people from entering, including razor wire and Jersey barriers, were being set up at the port. "After the materials are in position, CBP will resume processing northbound vehicle traffic in select lanes at the border crossing," CBP said.

In a follow-up email, a CBP spokesperson confirmed the shutdown was being done to prepare for the potential arrival of thousands of additional people at the border.

“U.S. Customs and Border Protection (CBP) continues to prepare for the potential arrival of thousands of people migrating in a caravan to the United States through the Southwest border," according to the email. "Part of those preparations include installation of temporary impediment measures at and between the Ports of Entry, such as concertina wire or Jersey barriers."

Travel flowing southbound was unaffected by Monday's move. People crossing on foot were directed to the Pedestrian West facility while the east one was closed.

Last week, CBP shut down a few lanes at San Ysidro and the nearby Otay Mesa port to install and pre-position similar blockades.

CBP did not state how long all northbound traffic was suspended Monday.

CBP Commissioner Kevin McAleenan told reporters at a recent press conference announcing a troop deployment that some migrants who are unable to apply for asylum at ports due to limitations in the number of people officers can process in a day might instead choose to illegally enter the country.

An estimated 1,700 people were apprehended and deemed inadmissible at ports of entry each day in October across the entire southern border.

The possibility of thousands of people descending on one port or section between ports prompted the Trump administration to send thousands of troops to the border as reinforcements.