SAN DIEGO (AP) -- Walking into Mexico at the nation's busiest border crossing with the United States is no longer an uninterrupted stroll for foreigners.

Starting late Wednesday, pedestrians going to Tijuana from San Diego at the San Ysidro crossing must choose between a line for Mexicans who get waved through, and a line for foreigners who must show a passport, fill out a form and - if staying more than a week - pay 322 pesos, or roughly $20, for a six-month permit.

About a dozen foreigners stood in line Wednesday night, directed by English-speaking agents to six inspection booths where they got passports stamped. It took about 10 minutes from start to finish.

Travelers have long followed similar protocol at Mexican airports, but the new border procedure marks a big change at land crossings that weren't designed to question everyone. Pedestrians and motorists have generally entered Mexico unencumbered along the 1,954-mile border with the United States.

"This is about putting our house in order," said Rodulfo Figueroa, Mexico's top immigration official in Baja California state, which includes Tijuana.

The changes, which have been in the works for years, come as Donald Trump has surged to the top of the Republican field in the U.S. presidential race. He has insisted that Mexico sends criminals to the U.S. and pledges to build a border wall at Mexico's expense.

For Mexico, it is a step toward closing an escape route for American criminals who disappear in Mexico. Border inspectors will tap into international criminal databases. Motorists will see no change, and if lines get too long, officials will also wave pedestrians through.

More than 120 Americans expelled from Mexico this year while living in Baja California had arrest warrants in the U.S., according to Figueroa, delegate of the National Migration Institute. Some ordered to leave last year were on the FBI's most-wanted list.

But authorities say benefits extend beyond stopping unwanted visitors. A recent hurricane stranded twice as many Americans in Cabo San Lucas than U.S. authorities thought were there, Figueroa said, and registering as a foreigner would have made it easier to identify those who needed help.

Figueroa said Mexico can initially process about 1,000 foreigners daily, up from about 50 currently.

"If the line becomes clogged up, we will just let everybody through," Figueroa said. "If we can't check everybody, we won't."

Figueroa said San Ysidro is believed to be the first U.S. land crossing to have a separate line for foreigners to show passports and that it will serve as a model for others as they are upgraded. Aurora Vega, a spokeswoman for the National Migration Institute, referred questions to other departments. Officials at the Foreign Relations Department and Mexican Embassy in Washington had no immediate comment.