SAN FRANCISCO (CBS SF) — Fire strike teams from the Bay Area are being assembled to head to Butte County to help battle a wildfire that has exploded in size since Thursday morning.

The so-called Camp Fire near Chico has burned at least 18,000 acres as of Thursday afternoon, prompting mass evacuations. An unknown number of injuries have been reported as well as a number of structures burned.

The San Francisco Fire Department has sent 22 firefighters, five engines and a battalion chief to the town of Paradise as part of an urgent-need strike team to protect structures.

San Mateo County was also putting together a strike team as of Thursday afternoon. The crews were to leave from Station 1040 on East Hillsdale Blvd.

Alameda, Marin and Sonoma counties have also sent crews to Butte County. The California Office of Emergency Services sent a strike team with firefighters from Oakland, Fremont, Hayward and Alameda County fire departments.

Crews from the Berkeley Fire Department and the Livermore-Pleasanton Fire Department were also headed to Butte County.

Marin County Fire said 62 fire personnel were already on scene, including the Marin Operations Area One Strike Team, one local government strike team, and the 24-person Tamalpais Fire Crew.