Police were called at approximately 20:30hrs on Thursday, 18 November to reports of a fire at a residential address in Hamilton Road, Bexleyheath.
London Fire Brigade and London Ambulance Service attended with officers.
Two adult women, and two children – believed to an infant boy and girl – were pronounced dead at the scene.
Their next of kin have been informed.
A man remains in hospital with injuries to his legs. His condition is not thought to be life-threatening.
A further person was taken to hospital by LAS after he arrived at the scene.
Next of kin are aware and receiving specialist support.
The deceased are all believed to have been related to each other.
At this early stage, the cause of the fire is not thought to be suspicious and there have been no arrests.
Detective Chief Superintendent Trevor Lawry, head of policing for Bexley, Lewisham and Greenwich said: “Our thoughts are with the family of the deceased, who have suffered such an awful and devastating loss. We have officers in the location and I know these sentiments are shared by residents across Bexley and London as a whole.
“Our inquiries are ongoing and we will continue to work with our colleagues in the London Fire Brigade to fully understand the cause of this terrible incident. In these very early stages we don’t believe the cause of the fire is suspicious.”