Detectives from the Specialist Crime Unit have launched a probe into the incident, in which the four people were said to have been found with stab injuries.
The Metropolitan Police were called to the scene at 1.40am today, after reports of a disturbance at a house in Bermondsey, Southwark.
A man has been arrested on suspicion of murder and remains in custody.
According to the force, all five people are believed to have been known to each other.
The victims, three women and a man, were pronounced dead at the scene.
A statement from the Metropolitan Police said: “Officers are in the process of contacting next of kin.
“Post-mortem examinations will be arranged in due course.
“A man has been arrested on suspicion of murder and taken to a south London police station where he remains in custody.
“Detectives from Specialist Crime are investigating.
“It is thought that all five people were known to each other.
“Enquiries continue to establish the circumstances.”
UPDATES TO FOLLOW…