Updated

The busiest border crossing in the United States has officially closed for the weekend to travelers who normally drive through it daily to Mexico.

The San Ysidro Port of Entry connecting San Diego to Tijuana closed at 3 a.m. Saturday and will remain closed until noon Monday for work on a $741 million expansion project.

The expansion is believed to be the largest renovation of a crossing along the nearly 2,000-mile-long U.S.-Mexico border. It has been in the works for years to ease congestion and boost cross-border commerce.

Authorities have warned that the closure for southbound traffic may cause a massive traffic jam and become a monumental headache for border businesses, workers, tourists.

U.S. officials have advised drivers to use the much smaller Otay Mesa crossing to the east.