A police officer is fighting for his life after being injured in a confrontation with burglary suspects.
Eyewitnesses' reports suggest the officer may have been struck by a car after leaving his own vehicle following a high-speed chase, leaving him with critical head injuries.
Onlookers saw him lying in convulsions after another officer pulled a gun on the suspected getaway car.
Officers were called to reports of an aggravated burglary in Dagenham, east London, in the early hours of Saturday. The victim said the suspects were armed.
They escaped the scene in a silver Chrysler, which failed to stop for officers in an armed response vehicle in Stratford town centre.
Police followed the vehicle in the direction of Leytonstone High Road and a man made off on foot when it stopped briefly.
But the suspects reached a dead end in Ashlin Road, Newham.
It was then that an officer in his thirties, a member of the Met Police's CO19 firearms unit, left the armed response vehicle and sustained serious head injuries.
The Chrysler swerved around the marked police car and sped off, rounding the corner into Dunmow Road only to crash head on with another police vehicle.
Two other police officers, both Newham borough police constables, sustained minor injuries in the collision.
The three people in the Chrysler - a 26-year-old man, 19-year-old man and a 21-year-old woman - were arrested and taken to east London police stations, where they remain in custody.