A group of travellers moved onto the former Woolworths site off Faraday Road in Dorcan at the weekend.
In total there are about eight caravans, with some outside the entrance gate of the derelict land and more inside.
The land is privately owned so the police have been in contact with the landlord about the next course of action.
Another group of travellers also moved onto empty land at the old Fitness First site on Eldene Drive but they had moved on by this morning.
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