California Bridge Fire updates: Newsom expands emergency due to 'extreme behavior'

The Bridge Fire straddling Los Angeles and San Bernardino counties was late Wednesday the largest wildfire in California, as authorities battled several large blazes aided by federal assistance and the state National Guard.

Some 2,500 structures are under threat from the Bridge Fire, Cal Fire said in its latest Wednesday night update, with the wildfire consuming 50,258 acres and at 0% containment.

The blaze -- the cause of which is still undetermined -- "continued to exhibit extreme fire behavior" through Wednesday, Cal Fire said, growing by 13,000 acres "mainly on the north and east flanks."

At least 13 structures were destroyed in the Wrightwood area, with power infrastructure also affected. Mountain High West and East Ski Resort were both affected by fire activity, while 20 homes in Mount Baldy and six wilderness cabins were destroyed.

Cal Fire warned that the expanding inferno may cause "spot fires" as it reaches areas of "receptive fuels with little to no fire history."

The Bridge Fire is one of three large wildfires active in southern California. The Airport Fire -- straddling Orange and Riverside counties -- continued to burn on Wednesday, at 23,140 acres with 5% containment.

Though firefighting crews ensured minimal growth of the blaze through Wednesday -- partially thanks to improved weather conditions -- two civilians and 10 firefighters have so far been injured.

Evacuation orders are in place for 5,513 homes in Riverside County, and evacuation warnings in place for 9,581. Some 53,000 Riverside County residents are affected by the fire.

wildfire map:

Gov. Gavin Newsom traveled to southern California on Wednesday, proclaiming a state of emergency in Los Angeles, San Bernardino, Orange and Riverside counties in response to the Bridge and Airport fires, his office said in a press release.

Newsom declared a state of emergency related to the Line Fire last weekend. That wildfire -- east of Los Angeles in San Bernardino County -- was 18% contained as of Wednesday night, Cal Fire said, at 36,481 acres in size.

More than 100,000 people have been displaced from the affected area amid evacuation orders and warnings, with 65,600 structures threatened. One arson suspect was detained earlier this week on suspicion of starting the blaze.

Newsom visited the Line Fire command post in Highland on Wednesday.

"California is deploying every available resource to combat these devastating fires, and we'll continue to work in lockstep with federal and local partners in this herculean effort," Newsom said.

ABC News' Marilyn Heck contributed to this report.