Police are treating two fires at a derelict factory in Co Tyrone as arson.
Substantial damage was caused to the former Herdman's Mill in Sion Mills after separate blazes were started on Friday and Saturday.
A spokesman for the Police Service of Northern Ireland (PSNI) said: "We are treating these fires as arson and I would appeal to anyone with information to contact police in Strabane on 101."
Members of the public have also been advised to stay away from the building, which is in danger of collapse.
The PSNI spokesman added: "This building has been condemned and under no circumstances should anyone enter the building due to health and safety concerns and a high risk of serious injury."