An individual reportedly "brandished a knife" in downtown Derby on Sunday night.
Armed police officers were arrested as a result of reports of an armed man on the street during an altercation.
A man was arrested by police and a knife was found by police dog Zane a few blocks away, Derbyshire police said.
In a tweet, Derbys Dog Section said: "A man from downtown Derby wielding a knife in the street." Safely detained by @DerbyshireARU at the scene.
"PD Zane is deployed to search for the exceptional offending weapon, landmarks and indicates on this knife some streets further #OneTeam #TheNoseKnows."
The Derbyshire Armed Response Unit said: "Supporting Operation Helping @DerbyResponse – Another Knife Incident.
"Male was not compliant and had to be restored." Knife involved, we can not afford to take risks.