The extent of the damage in the morning light after the former Foyle College was deliberately set on fire on a previous arson attack
The NI Fire and Rescue Service received the first reports of a fire at 7.31 pm on Saturday.
Three NIFRS appliances, including one aerial unit, remain at the scene on Sunday morning.
Nearby residents have been advised to keep their windows closed and to bring pets indoors because of the smoke.
Five NIFRS appliances were initially sent to the scene on Saturday night.
The Duncreggan Road remains closed to traffic.
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