One man has died and a second man has been seriously injured following a double stabbing.
Police and paramedics were called to the incident in Gilpin Street, Peterborough, at 7.17am on Wednesday.
One man died at the scene and a second man was taken to hospital where he is described as stable.
Detective Inspector Tim Redfearn said: "Details about this incident remain sketchy and I would like to hear from anyone who was in the area this morning, who has any information about this incident."
An East of England Ambulance Service spokeswoman said: "Our thoughts are with all those affected by this incident.
"Our crews worked extremely well with other emergency services on scene in an extremely difficult situation and the trust thanks them for their sterling efforts."
Witnesses should contact the Cambridgeshire Police major crime unit on police non-emergency phone number 101.