350-acre brush fire burning near buildings in Fontana

A 350-acre brush fire is threatening some buildings in Fontana near the Jurupa Hills Regional Park area. 

The fire, which is being referred to as the Sierra Fire, was first reported at about 3:30 p.m. near Sierra Avenue, south of the I-10 Freeway, according to San Bernardino County Fire Department officials. 

It quickly grew from just one acre to 40 acres by 4 p.m. and again jumped to 350 acres by 6:30 p.m., prompting a second alarm response from firefighters including support from Riverside County Fire Department. 

At the latest it is 15% contained, according to San Bernardino firefighters. 

The fire is spreading southeast "with moderate side slope expansion to east," firefighters said. 

Crews have set up in front of homes in the area in the event that the fire moves towards them. 

As a result of the firefight, Fontana police have shut down Sierra Avenue at Jurupa Avenue to the public. 

Crews say that structures are threatened by the spreading flames, but no evacuation orders have yet been issued. 

This is a developing story. Check back for details.