Fire fighters and police were called to Mount Annan High School just after 3am this morning after reports a fire had broken out at the school.
Fire and Rescue NSW (FRNSW) Narellan'sRescue Pumper along with Fire and Rescue NSW Camden and Campbelltown were alerted and arrived on scene within minutes.
Camden Police Area Command were already on the scene and told fire fighters there was a fire in a science lab.
Fire and Rescue NSW Narellan said on its Facebook page that "early intervention by NSW Police Force assisted [them] in locating the fire quickly."
"Crews gained entry and rapidly attacked the seat of the fire using high pressure hose lines," the post said.
"The fire was contained to the room of origin and the area given an all clear from HAZMAT technicians from Fire and Rescue NSW Rosemeadow."
The classroom sustained a substantial amount of smoke damage to the walls and furniture.
A blunt object was used to damage 12 windows to the science block of the school.
Officers from Camden Police Area Command have established a crime scene.
Police believe the fire was deliberately lit.
The cause of the fire is still under investigation.
FRNSW St Andrews, Horningsea Park and the Duty Commander from FRNSW Macarthur Region Command also attended as part of a second alarm response from FRNSW.