Cal Fire crews Friday morning were preparing to send strike teams into Mexico to help fight a 1,500-acre brush fire near Tecate, officials said.
The blaze was 30% contained after firefighters worked on containment lines overnight, Cal Fire said in a tweet.
The fire, reported Wednesday afternoon, sent up a huge plume of smoke visible for miles, prompting Cal Fire to send in air tankers to make drops just north of the border.
Flames crept through rough, hilly terrain but had not jumped the border, Cal Fire tweeted.
Cal Fire crews are also fighting a blaze near Dulzura, holding it at 80 acres with 25% containment as of early Friday, official said.
No structures were reported threatened in either fire.