Classrooms burnt at Blue Mountains school

A school affected by last year's bushfires in the NSW Blue Mountains was ablaze again on Sunday.

Four classrooms were destroyed and a fifth damaged in a suspicious fire at St Columba's Catholic College in Springwood, which is surrounded by extensive bushland.

Wood work, metal work and home economic classrooms towards the back of the school have been destroyed.

No one was injured.

HSC assignments were lost but thankfully they had been marked, Police Minister Stuart Ayres said.

The board of studies and Catholic Education Office will support the school in preparation for upcoming HSC exams.

Mr Ayres had strong words for the alleged arsonist.

"You are of the lowest form of human being that anyone in this state would know," he said.

Police were called to the school at 5am and 12 firefighting crews from NSW Fire and Rescue and the Rural Fire Service surrounded the building to battle the blaze.

After being brought under control on Sunday afternoon, investigations into the cause will continue as fire smoulders underneath the rubble.

Police were using a cherry-picker crane to investigate the blaze as the walls could collapse any minute.

The school had prepared itself for the bushfire season by installing water tanks and a high pressure pump, which Mr Ayres said were critical in battling the blaze.

"Had that system not been installed, there would have almost certainly been a loss of more buildings," he said.

More than 200 homes were destroyed in last year's blaze.