Officers were called at 07:15hrs on Wednesday, 31 July to Cundy Road, E16, to reports of a man in the middle of the road assaulting people.
It was then reported that the same man was walking off, towards Prince Regents Lane. Further reports were received that the man was acting irrationally, throwing himself on to passing cars and confronting council workers.
The man was then reported to be running towards the Excel Centre. Officers attended and found the man being restrained by security staff at the centre.
The man was placed in handcuffs by officers, but became unresponsive.
Officers immediately administered first aid and London Ambulance Service were called.
Police are in the process of informing his next of kin.
The man, believed to be aged 37, was taken to an east London hospital where he died a short while later.
A post-mortem examination will be held in due course. Formal identification awaits.
A member of the Excel security staff was treated at hospital for bite injuries. No arrests have been made.
Two forensic scenes are in place, at Prince Regents Lane and the Excel Centre.
Road closures are in place. Enquiries into the full circumstances continue.
As is routine, the Directorate of Professional Standards have been informed.
The Independent Office for Police Conduct has also been notified.