Crews with the San Bernardino County Fire Department are on the scene of a wind-driven brushfire in Fontana that has grown to an estimated 350 acres and is threatening structures, authorities confirmed to KTLA.  

The two-alarm blaze, dubbed the “Sierra Fire,” was first reported around 3:30 p.m. in the area of 11660 Sierra Avenue behind Martin Tudor Splash Park, fire officials said.  

Amid warm temperatures and westerly winds blowing between 10-15 miles per hour, the vegetation fire, which was burning in what crews called “light fuel,” moved in a southeasterly direction with “moderate side slop expansion to [the] east,” and quickly grew to some 40 acres.

By 4:30 p.m., fire officials said crews and equipment were in place to protect the threatened structures.  

Just two hours later, the brushfire had grown to some 350 acres with 15% containment.  

“Additional ground resources and aircraft requested,” fire officials said on X, formerly Twitter.  

So far, it does not appear that any mandatory evacuation orders have been issued.  

The cause of the fire remains under investigation.  

This is a developing story. Check back for additional updates.