Massive wildfire burns in southern California

A massive wildfire continues to burn in southern California.

The fire spans 17,305 acres in the San Bernardino National Forest, California officials said Sunday. The blaze – which is 21% contained – has already cost $5 million, according to NBC Los Angeles. About 500 structures have been listed as “threatened,” according to officials, but none so far are believed to have been damaged or destroyed.

The cause of the 25-square-mile fire, which was first reported on June 17, remains under investigation. Nearly 2,000 firefighters and other responders are currently battling the blaze, according to NBC News.

Below are photos of the massive fire.

Trees are covered in smoke as a fire continues to burn, June 21, 2015, in Angelus Oaks, Calif. Firefighters working amid sweltering conditions in steep terrain were aided by a fleet of water-dropping aircraft in attacking flames in the mountainous wilderness about 90 miles east of Los Angeles.

Photo by Micah Escamilla/The Sun/AP

A crew member from the Big Bear Hotshots lights a back burn at the Lake Fire in the San Bernardino National Forest, Calif., early on June 20, 2015.

Photo by Stuart Palley/EPA

A tree burns at the Lake Fire in the San Bernardino National Forest, Calif., June 20, 2015.

Photo by David McNew/Reuters

A firefighter helicopter flies near the Lake Fire in the San Bernardino National Forest, Calif., June 19, 2015.

Photo by David McNew/Reuters

Members of El Carrizo Hot Shots crew cut fire a line through the night to try to contain the Lake Fire in the San Bernardino National Forest, Calif., June 19, 2015. 

Photo by David McNew/Reuters

Flames spread through the forest in the Lake Fire in the San Bernardino National Forest, Calif., June 19, 2015.

Photo by David McNew/Reuters

A firefighter monitors a wildfire as it spreads to the road near Jenks Lake in the San Bernardino National Forest, Calif., June 18, 2015. 

Photo by Lucy Nicholson/Reuters

A helicopter makes a water drop on a wildfire near Jenks Lake in the San Bernardino National Forest, Calif., June 18, 2015. 

Photo by Lucy Nicholson/Reuters