Suspicious fire at Sydney high school

A fire that destroyed part of a high school in Sydney's west is being treated as suspicious.

Fire crews were called to Bossley Park High School in the early hours of Friday to find a staff amenities and store room, which contained computers, alight.

Four fire crews contained the blaze in the two-level building before it spread to any classrooms, Fire & Rescue said.

The staff room has been destroyed while other rooms have substantial smoke damage.

The cause of the fire has been deemed suspicious and police are investigating.

The school is open to students.