A youth was taken to hospital after he fell through a skylight in an empty derelict school building in Llandudno Junction.
Three young males were seen running from the closed Nant-Y-Coed School on Ronald Avenue, Llandudno Junction, on Saturday.
North Wales Police officers attended the scene where they found the fire door had been opened and the skylight had been broken.
Officers visited a nearby address following the incident where a juvenile confirmed that he had fallen through the sky light after being on the roof.
Police have put out a warning of the dangers of going into derelict or closed buildings.
PC 3074 Mike Smith said: “Fortunately this boy was not seriously injured, but youngsters should be reminded of the dangers of climbing onto the rooves of empty and derelict buildings.
“We urge people who live close to an empty or derelict property to be aware and to be vigilant, watching out for any suspicious activity.”
Anyone who sees someone acting suspiciously in their area is asked to call 101.
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