Update Thursday:
Miranda police are treating a fire at the former Caringbah High School last week as suspicious.
Miranda crime manager Shane Woolbank said they had no suspects but teenagers were seen in the area shortly before the blaze.
Police have also approached Sutherland Shire Council about a demolition order for the site which they say is derelict and unsafe.
Saturday:
Emergency services have put out a fire in a derelict block on the former Caringbah High School site.
Police and Fire&Rescue NSW were called in at 3.15pm Saturday and found the building on Willarong Road well-alight.
They said the building, a former high school, is abandoned and no one was inside at the time. The roof was destroyed.
The fire was in the southern section of the high school which was abandoned several years ago when the school was consolidated at the northern end of the site.
It is the second time a building in the area has caught fire. In April 2013 a witness told police they saw two boys running from the site shortly before smoke started seeping out of the empty building. They were not wearing school uniforms and no further description was given. See related story: http://www.theleader.com.au/story/1403993/old-caringbah-school-site-fire-suspicious/
Miranda police and the Traffic & Highway Patrol Command were at the scene on Saturday and closed surrounding streets.
No one was injured and there was no threat to surrounding buildings.
Members of the public are urged to avoid the area.
Inquiries continue, anyone with information should phone police on Crime Stoppers on 1800 333 000.
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