Five Metropolitan Police officers were injured when a dog attacked them in east London.
Officers from Newham went to an address in Albert Square, Stratford, to make an arrest when they were attacked at about 09:00 GMT.
Four of the officers suffered serious injuries and the fifth PC has minor injuries.
The animal, described as a pitbull-type dog, was shot dead. A man in his 20s, has been arrested.
He remains in custody in an east London police station.
The injured officers are all in a stable condition in hospital.
A dog unit and armed officers from CO19 Specialist Firearms Command were called to the scene following the attack.
The animal was contained before being shot.
(courtesy BBC News 22 March 2012 Last updated at 14:45)