MORENO VALLEY, Calif. >> Firefighters in Southern California were battling three separate brush fires that started Friday afternoon amid a blistering heat wave.

The fires were all within 40 miles (65 kilometers) of each other in mostly rural areas across Riverside County, southeast of Los Angeles.

Nearly 1,000 homes were under evacuation orders, but there were no immediate reports of injuries or property loss, according to officials from the California Department of Forestry and Fire Protection, known as Cal Fire.

Two of the fires had stopped spreading by the evening. The third, though, grew at a “rapid rate” to more than 2 square miles (5 square kilometers) in a matter of hours, Cal Fire said in a social media post.

Hundreds of firefighters were dispatched.

California is bracing for its hottest weather of the year so far this weekend, and Riverside County is among areas under an excessive heat warning.

Already blistering temperatures are forecast to go even higher for Nevada, Arizona and California, soaring in some desert areas above 120 degrees Fahrenheit (48.8 degrees Celsius) during the day and remaining in the 90s (above 32.2 Celsius) overnight.

California leaders warned earlier in the week about the fire danger.

“As we get deeper into the summer and vegetation that grew up during the wet spring dries out, we are seeing an uptick in wildfire activity,” California Natural Resources Secretary Wade Crowfoot said at a Wednesday news briefing.

The causes of all three fires are under investigation, Cal Fire said.