Five fire appliances were tasked to the Rockmills flats complex in Derry following a fire in the block on Monday.
An ambulance was also dispatched to the scene.
A Northern Ireland and Fire Rescue Service spokesperson said five fire appliances - two from Northland Road, two from Crescent Link and one from Strabane - responded to a call out at 9.10 a.m.
"Firefighters attending a fire in a fourth floor apartment. The incident is currently ongoing," said the NIFRS spokesperson.
The Northern Ireland Ambulance Service (NIAS) said it received a 999 call at 9.22 a.m. on Monday.
NIAS dispatched one emergency crew and one 'Hazardous Area Response Team' to the scene.
Following assessment and initial treatment at the scene, no one was transferred to hospital.