The police and fire service say youths are known to have entered a building they still consider to be unsafe after a large fire on Thursday.
They have asked people to stay away from Peebles High School while investigations continue into the fire there.
The fire is thought to have begun in the gym and the roof has collapsed. Police say it's a hazardous and unsafe environment and youths that have entered the building have put themselves at risk and action will be brought against anyone found on site.
Police Scotland's Chief Superintendent John McKenzie said: "We are aware of youths who have entered the building, placing themselves at risk. This is a hazardous and unsafe environment for anyone to be in. We would ask parents and carers to assist us; talk to your child about the potential dangers and the consequences as this could make a difference to their safety. "
She continued: "We will take action against anyone found within the site. We are continuing to carry out investigations into the fire, along with Scottish Fire and Rescue Service."
Area Commander Stephen Gourlay from SFRS says: "Not only is this site a dangerous environment for anyone to be in at this time, it also remains a live incident ground with SFRS resources and our partners in attendance.
"We would therefore urge everyone to stay away from the site for their own safety and to allow us and our partners to carry out our investigations and ensure the area is made as safe as possible.
"We will work to ensure as many people as possible are aware of the risks, however the community can play its part by helping to spread the message, particularly if they think someone may be thinking of entering the site."
The school says it understands people may wish to collect their belongings and will make arrangements when the building is safe.
Tracey Logan, Chief Executive of SBC: "It is extremely dangerous for anyone to come close to, or try and enter, any part of the school. I cannot stress enough how important it is to remain well clear of the school site at this time.
"I understand that people are keen to get back their belongings that may have been left behind during the evacuation. I can assure everyone that we are working on arrangements but we can't do this until emergency services give us full access to the school. We will communicate details on this as soon as possible via Groupcall, on our website and social media channels."
Parents are asked to talk to their children about the dangers. It's still not known when the 1200 students can return to school.