A police officer has been stabbed in the head by a man who had picked up a baby.
A 20-year-old man has been arrested on suspicion of attempted murder.
Police were responding to a call about a violent man armed with a knife who had picked up the infant when the stabbing happened.
The Metropolitan Police have launched an investigation into the attack in Walworth, south-east London, shortly after 8pm yesterday.
A Scotland Yard spokesman said: "Officers attended the address and attempted to speak to the man. The man put the baby down but subsequently attacked the officers present."
A male Pc in his 30s suffered stab injuries to the shoulder and head and was taken to hospital. He has since been discharged.
The 20-year-old man is in custody at a south London police station.