A runner taking part in the Hackney Half Marathon was treated by emergency services at the event, and later died in hospital.
The annual 13.1 mile race takes competitors on a route around the borough, with this year's event taking place last Sunday (May 22).
Organised by Limelight Sports Club, the race is one of many fitness activities put on for the weekend-long Hackney Moves festival.
The club expressed its condolences in a statement released following the death: "We are greatly saddened to share that a participant in the Hackney Half has passed away.
"We are in close contact with the runner’s family and offer our deepest condolences and support.
"To respect the privacy of the participant’s family and friends, we will be making no further comment at this time."
A London Ambulance Service (LAS) spokesperson "a number of people" were treated over the course of the day.
They added: "One participant was treated by London Ambulance Service and St John Ambulance at the scene and conveyed to hospital, where later they sadly died.”
No further details have been released.
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