Firefighters with Cal Fire San Diego are battling a wildfire near the U.S.-Mexico border east of the Otay Mesa Port of Entry.
The fire grew to six acres on Otay Mountain and was not posing a threat to structures, Cal Fire said.
"Firefighters are making good progress," the agency said.
By 4 p.m., the forward rate of spread had been stopped but firefighters would remain on scene through the night to build a containment line.
Due to the topography of the area, the flames were fought by air with the help of helicopters and firefighters.
Images from SkyRanger7 showed fires on both sides of the border. A spokesperson for a fire agency in Mexico confirmed the fires were separate. Black smoke was rising near the Tijuana to Tecate highway in Mexico.