U.S. immigration officials will begin returning as many as 20 migrants per day to Mexico through the San Ysidro border crossing in San Diego as they await an answer to their asylum applications, the Mexican government said on Friday.

U.S. officials want to expand the practice, which represents a major immigration policy shift in both countries, to all other entry points along the border, said Roberto Velasco, a spokesman for Mexico's foreign relations ministry.

"The Mexican government does not agree with this unilateral measure" but will accept most migrants under certain conditions, Velasco said.

Velasco said at about mid-day Friday that the first 20 migrants would be sent to Tijuana "in the next few hours." He said the Mexican government would receive most asylum applicants, unless they're unaccompanied minors or sick. The Mexican government will consider the cases of entire families sent back individually, Velasco said.

Asylum applications can take months or years, and Mexico's president and top foreign relations and immigration officials have given contradicting statements on whether the country is prepared to receive applicants from the U.S.

U.S. immigration officials plan to bus the asylum seekers back and forth across the border for hearings in downtown San Diego, Velasco said. It is unclear whether they will have access to attorneys in the U.S.

All applicants are from Central America, Velasco said.