More than 35,000 structures threatened by wildfire burning east of Los Angeles

More than 35,000 structures were being threatened Sunday by an out-of-control wildfire in Southern California that has prompted evacuation orders and an emergency declaration by the governor, officials said.

The Line Fire, which ignited Thursday in the foothills east of San Bernardino, had burned 17,459 acres by Sunday morning and was 0% contained, according to the California Department of Forestry and Fire Prevention (Cal Fire). Numerous single- and multi-family homes were among the structures being threatened by flames, officials said.

Officials began issuing mandatory evacuation orders and warnings and declared a local emergency after the blaze grew to more than 7,000 acres on Saturday. One of the evacuation orders was issued due to "an immediate threat to life" in an area of San Bernardino County from Calle Del Rio to Highway 38, including Greenspot Road North, the San Bernardino County Sheriff's Office said in a statement.

Gov. Gavin Newsom also declared a state of emergency for San Bernardino County on Saturday, saying in a statement that California had secured assistance from the Federal Emergency Management Agency to help suppress the fire. The request was approved by President Joe Biden on Saturday afternoon, Newsom said.

"I thank President Biden for his swift approval of support for the work of our firefighters and first responders battling this fire and protecting local communities," Newsom said. "It's critical that residents in the impacted areas remain vigilant and prepare to evacuate immediately if called for by local authorities."

At least three firefighters have been injured battling the blaze, according to Cal Fire.

As of Sunday morning, no structures had been damaged or destroyed, Cal Fire reported.

The cause of the fire remains under investigation.

The fire is being fueled by "critically dry" vegetation in the area and thunderstorm outflow winds that are "causing very erratic behavior on the Line Fire," according to Cal Fire.

Making fighting the blaze more challenging for fire crews was the excessive heat enveloping Southern California, officials said.

"Today there will be a slight chance of showers and thunderstorms over the fire area. Temperatures will range from the upper 80s to around 100 degrees and an Excessive Heat Warning continues throughout the day," Cal Fire said in an updated statement Sunday.

More than 620 firefighters were battling the blaze Sunday, including four firefighting helicopter crews, according to Cal Fire.

The Line Fire is one of 14 active wildfires burning in California as of Sunday, according to Cal Fire.

The Roblar Fire

Among the other wildfires scorching California was the Roblar Fire, which started Saturday afternoon near the Marine Corps Base Camp Pendleton in San Diego County. The blaze had grown to 856 acres by Sunday morning, burning mostly dry brush, according to Cal Fire.

The Roblar Fire was 0% contained on Sunday.

The Davis Fire

Another large wildfire burning in the West is the Davis Fire, in Washoe County, Nevada, near Reno, officials said.

The Davis Fire has destroyed 12 structures, burned 1,500 acres and caused authorities to close part of Interstate 580, officials said. Nearly 10,000 electrical customers were without power due to the local utility company, EV Energy, de-energizing powerlines in the area to prevent the spread of the fire, officials said.

Red Flag fire conditions for Washoe County are in effect until at least 8 p.m. PT Sunday, officials said.

ABC News' Amanda M. Morris contributed to this report.