Migrants, who are part of a Central American migrant caravan, leave Mexicali for Tijuana, Mexico. (AP)

Central Americans seeking asylum in the United States will have to wait in Mexico while their cases are reviewed under a new plan called "Remain in Mexico," The Washington Post reported Wednesday.

Asylum seekers have historically been allowed to stay in the U.S. while their cases are processed without fear of being deported. Under the new measures, asylum seekers will have to prove a "reasonable fear" of persecution in Mexico in order to gain entry. The new measure could go into effect as soon as Friday, the report said.

A Mexican official told the paper that under current law, Mexico does not allow those seeking asylum in another country to stay there during the process.

The Post's report was based on "internal planning documents" and three unnamed officials in the Department of Homeland Security. The paper called the proposal a major break from the current system, where asylum seekers have to establish a fear of returning to their home country. President Donald Trump has called the current system "catch and release."

A spokeswoman from DHS told the paper that there are no immediate plans to implement the measure. U.S. Citizenship and Immigration Services will reportedly send teams from various cities to port entries to begin the process.

At least 3,000 migrants have arrived in Tijuana, a border city across from San Diego, Calif., in the past two weeks. The federal government estimates the number of migrants could grow to 10,000 in the coming weeks, or months.

Those already in the city have camped out in tents, slept on dirt fields or under bleachers or are staying in overcrowded shelters throughout the city as they wait to figure out their next steps.

But some are growing impatient, and believe their best option is to plan a mass crossing.

“Most of us, yes, we want to be on the other side,” Jorge Molina, a Honduran migrant, told Telemundo. “Some want to jump over the wall, others to go another way, and others want to wait and see what kind of response they get.”

About 5,800 active-duty troops dispatched to the border to deal with the migrant crisis started coming home this week. On Monday, a judge barred the president from enforcing a ban on asylum for those who cross the U.S. border illegally – a decision the administration said would cause “countless illegal aliens to pour into our country."

Fox News' Carolyn Salazar contributed to this report