A large fire at a disused factory in Bangor, Co Down on Saturday night was arson, say police.
The Northern Ireland Fire and Rescue Service (NIFRS) tackled the blaze at Faulkner Road, off the Clandeboye Road, shortly before midnight.
As emergency crews were alerted to the scene the PSNI advised nearby residents to keep windows and doors closed to avoid a health risk from smoke.
NIFRS group commander Randy McComb told the BBC: "It was a very well-developed fire and it's a very large building - about 100 metres by 60 metres.
"The fire was right through the roof when we arrived, it took eight appliances to deal with the fire and it took us about six hours to bring the fire fully under control.
"We still have a crew there at the moment and we have a fire investigation team there at the moment trying to determine the cause of the fire.
"Thankfully nobody was injured."
Crews left the scene at around 9.30am Sunday.
Police have appealed for information, saying "at this stage the fire is believed to have (been) started deliberately."
Witnesses or anyone with information should call the non-emergency number 101 or Crimestoppers anonymously on 0800 555 111.
Due to fire off Clandeboye Rd, Bangor residents asked to keep windows & doors closed to avoid health risk with large volumes of smoke.— PSNI (@PoliceServiceNI) August 2, 2014