Police were called to reports of a shooting in Tottenham, north London, at 9.35pm on Monday.
Officers found the teenage girl with a gunshot wound in Chalgrove Road, a residential street near Northumberland Park station.
"Despite the best efforts of the London Ambulance Service, she was pronounced dead at the scene at 10.43pm," a Scotland Yard spokeswoman said.
"Her next of kin are aware and a crime scene is in place. No arrests have been made at this stage."
Neighbours said they heard gunshots at around 9.30pm on Monday. One witness, who works in a nearby shop, said he heard three bangs which sounded like fireworks.
He said he saw the victim sat with friends following the shooting before police cars and ambulances arrived. He also saw blood on the right side of the 17-year-old's chest.
Another neighbour described the murder as "very sad". She said: "I heard the bangs because I sleep in the front room. I thought it was a bomb.
"It's not nice - so many drugs, stabbings, cycles up and down - no respect for people any more."
Less than half an hour after the alarm was first raised in Tottenham, police were alerted to another shooting around three miles away in east London which left a 16-year-old boy fighting for life.
Scotland Yard said it was called to reports of gunfire in Markhouse Road in Walthamstow at around 10pm.
On arrival they found two young victims suffering from gun shot and knife wounds.
The spokeswoman said: "A 16-year-old boy was found with gun shot injuries. He has been taken to an east London hospital where he remains in a critical condition. THINK YOUR FRIEND WOULD BE INTRESTED? SHARE THIS STORY USING ANY OF THE SHARE BUTTON BELOW ⬇ PLACE YOUR TEXT ADVERT BELOW:>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>> ( FREE ) secret Fruits that Increased My Manhood size and Lasting Power in 7-days... CLICK HERE TO GET IT Warning To Men: This 3 Foods Is Killing Your Erection. Click Here To Know Them