Walking into Mexico at the nation's busiest border crossing with the United States is no longer an uninterrupted stroll for foreigners.
Pedestrians and motorists have generally entered Mexico unencumbered along the 1,954-mile border with the United States.
Now, pedestrians going to Tijuana from San Diego at the San Ysidro crossing must choose between a line for Mexicans who walk through unchecked, 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.
Travelers have long followed similar protocol at Mexican airports, but the procedure marks a big change at land crossings that weren't designed to question everyone and fully enforce that nation's laws.
"This is about putting our house in order," said Rodulfo Figueroa, Mexico's top immigration official in Baja California which includes Tijuana.
The switch went without a hitch on its first full day of operations Thursday. About a dozen foreigners stood in line, directed by English-speaking agents to six inspection booths. It took about 10 minutes from start to finish.
About 20 people were denied entry during a six-hour stretch because they had no passports. Agents exercised discretion to let others through with a warning to come prepared next time.
Susan Cox, who took a bus from Las Vegas to San Diego and walked across, was surprised but understanding.
"The more security, the better," Cox said as she headed to see her fiance, who was deported from the U.S. and lives in Tijuana. "Maybe they'll stop people coming into Mexico who are on the run, people who are a threat."
Others disapproved. Jesus Reynosa, a Tijuana taxi driver who caters to pedestrian crossers, said he has struggled for American customers after the 2001 terror attacks led to heightened U.S. border security — and longer lines — to return to San Diego and a spell of drug-fueled violence several years ago spooked tourists.
"We used to have thousands of Americans, now we have few. Soon we'll have even fewer," he said while waiting for customers.
Motorists will see no change, and if lines get too long, officials say they will also wave pedestrians through.
The changes, which have been in the works for years, came 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 he 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.
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 the 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.