Fire Commissioner Lloyd Ayers says the five-alarm fire at the Austin Manor Apartments in northeast Philadelphia injured 21 people early Sunday.
In a release Monday evening, Ayers said an open-flame candle in apartment B21 was to blame for the massive blaze.
Officials say three of the injured residents are in critical condition. Some residents were jumping from the building to escape the flames.
Fire officials say the four injured firefighters have all been treated and released from the hospital. All of the residents have been accounted for.
The fire broke out around 4:30 a.m. and was declared under control in about two hours.