Homes were evacuated following an arson attack at a block of flats in Downpatrick on Sunday morning.
The PSNI said the incident took place at a property in the Pegasus walk.
A police spokesperson said: “We received a report by colleagues from the NIFRS of a fire at a block of flats at around 9.30am.
“Residents in nearby houses and flats had to be evacuated, however no one was injured during the incident.
“This fire could have resulted in serious injuries, even loss of life and could easily have spread to the adjoining properties.”
They added: “We are treating this as arson with intent to endanger life and I am asking anyone with information, or who noticed any suspicious activity around that time, to contact us on 101 quoting reference number 811 of 18/07/21.”
Information can also be provided to Crimestoppers anonymously on 0800 555 111 or online at www.crimestoppers-uk.org