(CNN) -- A 500-acre brush fire burning on the Mexico-California border is a cause for concern Monday because of the weather, fire officials said.
The fire started on the Mexican side of the border Saturday and crossed into San Diego County near the Tecate port of entry, said Fire Captain Mike Mohler of the California Department of Forestry and Fire Protection.
"Tomorrow is supposed to be the hottest day of the heat wave [and we're] looking at triple digits in San Diego County," he said.
The fire is burning in the area of Bell Valley -- a rural region. It was not threatening any structures, Mohler said.
U.S. fire officials can cross a mile inside Mexico to assist with fire containment, Mohler said. They have to contact the U.S. embassy in Mexico if they need to go in farther, he said.