Some individuals who arrive at the San Ysidro port of entry, south of San Diego, starting Friday will be given notices to appear in court in the US and asked to remain in Mexico until then, the official told CNN on Thursday night.
The DHS official said the policy applies to migrants primarily from Central American countries.
Those with a "well-founded fear" of staying in Mexico, unaccompanied minors and certain vulnerable populations will be allowed into the US for their immigration proceedings.
In December, Homeland Security Secretary Kirstjen Nielsen announced that the US had told Mexico that individuals seeking asylum who enter the US illegally or without proper documentation would be sent to Mexico to wait for the duration of their American immigration proceedings.
US Immigration and Customs Enforcement will be responsible for transporting asylum seekers to and from American ports of entry for their court appearances. The first hearings are not expected to take place immediately.