Shots were fired at armed police from a car during a chase through the streets of east London.
Officers responded to reports of people armed with a gun in Lascelles Close, Leytonstone, at about 22:45 BST on Thursday.
Shortly after a car failed to stop for officers who set off in pursuit.
Scotland Yard said « a number of shots were fired towards officers » and police also opened fire. Three people have been arrested.
A spokesman from the Metropolitan Police said the trio arrested on suspicion of attempted murder had been taken to an east London police station and remained in custody. « The Directorate of Professional Standards has been informed as is routine, » he added.
The Metropolitan Police Federation, which represents officers in the capital, said the shooting highlighted « the dangers our members face. »