A teenager has been arrested on suspicion of attempted murder after two police officers responding to reports of a fight were stabbed.
Two other officers were also injured during the incident in Islington, north London, on Saturday night.
Police were called to reports of a fight in a home in Liverpool Road at about 10.45pm.
"Upon arrival, the officers were immediately met with hostility, with a man inside the address producing a large knife," the Metropolitan Police said.
The two stabbed officers were both men while two women officers were also injured - with one suffering a head injury and the other a suspected fractured wrist.
One remained in hospital being treated for stab wounds on Sunday morning.
Police recovered a knife from the scene and also arrested a second 19-year-old man, who was held on suspicion of affray.
Superintendent Mike Hill said: "This incident demonstrates the courage and professionalism officers show day in, day out in what can often be a dangerous job.
"When officers respond to what can often be a difficult situation or go to assist members of the public they should not be met with violence, it is completely unacceptable."