Scotland Yard confirmed that the 17-year-old girl died of her injuries after being stabbed at 12.16 pm near her home on Brisbane Street in Southwark.
The London ambulance service and ambulance were also called, but the teenager was pronounced dead at the scene.
The next of kin of the victim were made aware of her death.
A 21-year-old man was arrested for murder suspicion.
He is currently detained at a police station in South London.
Officers have confirmed that the man is known to the girl.
A crime scene lock is in place, but there are no road closures.
A spokeswoman for the Metropolitan Police said, "Police are investigating the death of a teenager in Southwark.
"The officers were called on July 12 at 12:16 pm at a residential address on Brisbane Street for reports of a stabbing.
"The London Ambulance Service and London Air Ambulance were also present, and despite all efforts, a 17-year-old girl was pronounced dead at 1,202
"The next of kin were informed.
"In due course, an autopsy will take place.
"A 21-year-old man – who was known to her – was arrested on suspicion of murder and is currently detained at a police station in south London.
"A crime scene is available at the address."
The spokeswoman added, "Met's Murder and Major Crime Command has been notified."
The victim is the 52nd, who has been stabbed to death in the capital since the beginning of the new year.