Evacuations were ordered Monday afternoon as firefighters battled two brush fires burning in the Angeles National Forest above Azusa and Duarte, amid a record-setting heat wave, fire officials said.

The first fire erupted around 11:15 a.m. on Highway 39 near the Morris Reservoir dam north of Azusa, according to the U.S. Forest Service. The fire is believed to have been started by a vehicle that went off the road.

The blaze, dubbed the Reservoir Fire, was first reported at 5 acres and rapidly spread to 1,200 acres, the Los Angeles County Fire Department said. No structures were threatened.

Mandatory evacuations were ordered for residents in the Mountain Cove, Rainbow Ranch, and El Encanto neighborhoods along Highway 39 in Azusa, according to the Azusa Police Department. Voluntary evacuations were recommended for the Mirador and Crystal Canyon neighborhoods. An evacuation center was set up at Memorial Park at 320 N. Orange Ave.

The second fire broke out about four miles away, near Opal Canyon and Brookridge roads, bordering a neighborhood on the foothills near Duarte. Fire officials said the so-called Fish Fire had scorched more than 2,000 acres and was moving north, away from homes.

Fire crews were attacking the flames by air and ground.

The fires erupted on the hottest day of a Southern California heat wave, as red flag warnings were in effect in the region through Tuesday.

Residents near to the Duarte Mesa fire were under mandatory evacuation orders from Markwood Street between Westvale Road and Tocino Drive, and above Conata between Tocino Drive and Mountain Crest Road. Mandatory evacuation orders were issued earlier for residents on Brookridge Road, with voluntary evacuations in effect for residents north of Fish Canyon Road from Greenbank Avenue to Encanto Parkway.

An evacuation shelter was set up at 1600 Huntington Drive in Duarte. Police said water and meals would be available, and service animals were welcome. Pet owners can take their small animals to Wonder Dog Ranch at 220 Taylor St. in Monrovia.

Large animals, such as horses, should be taken to the Pomona Fairplex at 1101 W. McKinley Ave, according to the Los Angeles County Sheriff's Department.

Monrovia residents whose homes are located north of Foothill Boulevard and east of Myrtle Avenue and the Bradbury area were advised that evacuations could be implemented, sheriff's deputies said.

By 9 p.m. Monday evening, the fires had not yet merged, and were 1.5 miles apart, according to the LA County Fire Department.