GUADALAJARA, Mexico — The U.S. government says it is working to "harden" the border crossing from Tijuana, Mexico, to prepare for the arrival of a migrant caravan leapfrogging its way across western Mexico.

Customs and Border Protection says it's closing four lanes at the busy San Ysidro and Otay Mesa ports of entry in San Diego, California, on Tuesday. It says it will install new infrastructure "in preparation for the migrant caravan and the potential safety and security risk that it could cause."

Thousands of Central American migrants left shelters in the western city of Guadalajara Tuesday to head by bus to a highway tollbooth to wait for rides to their next destination.