Photo: The Canadian Press

The busiest border crossing in the United States will close this weekend to the more than 40,000 cars that pass through it daily to Mexico.

The closure between San Diego and Tijuana for work on a $741 million expansion project presents a monumental headache for border businesses, workers, tourists and Christopher Enjambre. His band, Minor Gems, plays gigs in Tijuana.

"It's already hectic now, so ... damn," he said, shaking his head in disbelief. "It's going to be crazy."

Travellers have been enduring hours-long waits on the Mexican side of the border to enter the U.S. with the constant addition of security measures since the Sept. 11, 2001, attacks.

Frequent crossers, like Enjambre, 28, of Chula Vista, south of downtown San Diego, worry they will now face long lines on both sides, making trips through the San Ysidro crossing intolerable.

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.

U.S. officials are warning people to avoid driving to Baja California from 3 a.m. Saturday until noon Monday, hoping to ease what is feared will be a massive traffic jam on the U.S. side as Mexico-bound cars are detoured to the much smaller Otay Mesa crossing to the east.

"Don't even think about going across in a vehicle," said Jason M-B Wells, executive director of the San Ysidro Chamber of Commerce. "It's going to be a standstill."