A gang of up to 25 masked men, carrying guns and dressed all in black, were seen patrolling the streets of a Manchester suburb, police said.
Armed officers were deployed to Moss Side on shortly before 1600 GMT on Tuesday afternoon after reports of shots being fired by the men.
The gang was reported by five witnesses in Moss Side and Whalley Range.
They were seen on Withington Road, Carlton Road, Yarburgh Street, Great Western Street, and Barleycroft Street.
A police spokesman said officers searched the area but no further sightings of the gang were made.
He added there was no evidence of any firearms being discharged and there were no reports of injuries.
Extra patrols were stepped up in the area on Tuesday night.
Ch Supt Dave Keller said: "While on the face of it, this seems alarming, we had a lot of support around us.
"I was there myself and we had resources ready on the ground, and ample back-up.
"I would urge anyone who knows anything to come forward and they will be protected."
Anyone who may have seen the gang is urged to contact police on 0161 8564438.