High school badly damaged in Sydney fire

A fire has seriously damaged a high school in Sydney's west on the first weekend of the school holidays.

Emergency services were called to St Clair High School on Endeavour Avenue about 1.30am on Sunday and found several school buildings on fire.

The blaze ripped through science blocks, the canteen and a number of classrooms, police said.

Police have yet to determine if the fire is suspicious.

Investigators are due to examine the school on Sunday morning once the site is declared safe.

Officers are door-knocking surrounding homes in the hunt for witnesses.