East Sussex Fire & Rescue Service were called at 09.48 to a property in St Georges Road Brighton.
On arrival smoke was issuing from 1st floor.
Crews used breathing apparatus & hosereels to extinguish the fire.
The aerial ladder platform was used to reach 1 person & 3 others were led to safety.
A fire investigation into the fire has concluded it started accidentally in a kitchen, leaving the flat extensively damaged.
One person is being re-housed by the local authority.
Crews are providing home safety advice in the local area in the coming days using leaflets.