Authorities have arrested a male juvenile on suspicion of intentionally setting fire to Monrovia High School.
Officials say the fire was sparked early Monday inside the counseling office on the campus northeast of downtown Los Angeles. No injuries were reported.
KCBS-TV reports witnesses tell investigators they saw the boy throw something through a window before the fire started. Flames and black smoke erupted from the window.
Monrovia Police Sergeant Robert Wilkin told KPCC that damages could range anywhere from $500 to $1 million.
Police can't say if the boy is a student at Monrovia High. According to the principal, school will be open for classes as usual Monday morning as the investigation continues.
This story has been updated.