The fire broke out at Leyland St. Mary's Catholic Technology College in Lancashire around 4 p.m. Sunday -- just two days before the start of the school year, The Mirror reported.
Later in the day, police arrested five boys, ages 11 to 15, on suspicion of arson. The suspects were released on bail pending further inquiries.
A statement on the school's website said the fire caused "devastating damage."
"Please pray for the school at this difficult time," the statement said.
Firefighters were still working to put out small pockets of flames early Monday.
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