CIUDAD HIDALGO, Mexico – A growing throng of Central American migrants resumed their advance toward the U.S. border in southern Mexico on Sunday, overwhelming Mexican government attempts to stop them at the border. Their numbers swelled to about 5,000 overnight and at first light they set out walking toward the Mexican town of Tapachula, 10 abreast in a line stretching approximately a mile. Several hundred more already had applied for refugee status in Mexico and an estimated 1,500 were still on the Guatemalan side of the Suchiate River, hoping to enter legally. It was not immediately clear where the additional travelers had materialized from since about 2,000 had been gathered on the Mexican side Saturday night.