A flat fire in Derry's Waterside is being treated as arson with intent to endanger life, police have said.
Detectives from Strand Road police station are now appealing for information on the blaze which took place on the Dungiven Road.
A police spokesperson said that emergency services were alerted just before 6.45pm, and although no one was injured, "extensive damage was caused to the property".
"As enquiries continue, at this time, we are investigating this fire as arson with intent to endanger life," they said.
"I want to thank the member of public who raised the alarm. Had it not been for their actions, and the swift response from NIFRS colleagues, we could be dealing with a very different situation today."
Anyone with information about the fire ha been asked to get in touch on 101, quoting reference 1760 of July 27.
A report can also be made anonymously to Crimestoppers on 0800 555 111.