Arson attacks on disused Herdman's Mill in Sion Mills
Two fires at a disused factory in County Tyrone are being treated by police as arson attacks.
The first fire was started at Herdman's Mill in Sion Mills on Friday and caused "substantial damage", police said.
A second, at about 20:30 BST on Saturday, caused further damage.
Celia Ferguson, whose family owned the Herdman's factory, said that historical documents dating back 170 years were destroyed in the blaze.
Mrs Ferguson described the attacks as "horrifying".
"We have amassed one of the biggest sets of industrial archives in the world and thankfully a lot of the documents have been removed for preservation over the past 20 years. We don't know at this stage the extent of the destruction because we can't get near the building but it doesn't look good."
The mill was previously targeted by arsonists in October last year.
A police spokesman appealed to the public to stay away from the building, which carries "health and safety concerns and a high risk of serious injury".