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.”