A 14-year-old boy has been stabbed to death on a double-decker bus, police have said.
The victim was killed on the 472 bus on Woolwich Church Street near the junction with the A205 South Circular Road in Woolwich, south-east London, at about 14:30 GMT.
The teenager died at the scene shortly after paramedics from London Ambulance Service and the air ambulance arrived, the Metropolitan Police added.
No arrests have been made but a police cordon and road closures remain in place.
A London Ambulance Service spokesperson said: "We sent resources to the scene, including an ambulance crew, a paramedic in a fast response car, an incident response officer and a paramedic from our tactical response unit.
"We also dispatched London's Air Ambulance.
"Sadly, despite the best efforts of our crews, a teenager was pronounced dead at the scene."