The early morning blaze in Chapman Street, in Govanhill, Glasgow, is being treated as wilful fire-setting, according to the Scottish Fire and Rescue Service.
Crews were called to the address at 6am yesterday and evacuated the building of residents, including two adults and a child who were rescued from the first floor by ladder.
Twelve people were treated by paramedics at the scene but none were taken to hospital.
A fire service spokesman said: "We arrived and were immediately faced with a well-developed fire within the storage cupboard in the common close.
"There was heavy smoke logging within the close, affecting the means of escape for the residents.
"They quickly extinguished the fire using a high pressure water jet and assisted those residents who had self-evacuated."
Two appliances from Polmadie Community Fire Station and one appliance from Calton Community Fire Station responded to the incident.
Watch Manager Reid, the incident commander, said: "I committed six firefighters in breathing apparatus to tackle the fire and facilitate rescues in the building. Firefighters also rescued two adults and a child.
"Twelve residents were treated by paramedics at the scene but none of the residents were removed to hospital."