A wildfire in the hills near the U.S.-Mexico border exploded early Friday morning over thousands of acres, prompting evacuation orders throughout the Otay Wilderness Area and triggering school closures as well as likely power shutoffs for tens of thousands of people.

Border 2 Fire initially started 2:31 p.m. Jan. 23 in San Diego County. After being active for 20 hours, it has burned 5,389.4 acres, an increase of 1,139 acres since the last update. A fire crew of 692 effectively contained 10% of the fire by Friday noon. The blaze's cause remains under investigation.

The fires come as San Diego County mountains and valleys, along with other parts of Southern California, remain under a red flag warning.