Children across Newcastle have been targeted by pranksters dressing up as clowns and jumping out from behind bushes, police said.
It is thought to be inspired by a trend in America and officers said youngsters had been left "incredibly distressed".
Northumbria Police said it had received six separate reports since Friday, leaving parents concerned.
A spokesman said a teenager from Blakelaw had been arrested in connection with a "clown" incident.
He added a bladed article had also been recovered.
No-one has so far been injured, but the force has also received reports of clowns chasing people in the street.
Insp Stephen Wykes said: "The people carrying out these pranks may think they're being funny, but it is leaving a number of young people incredibly distressed.
"Parents of the children affected, and teachers at our local schools, are understandably concerned and we are working very closely.
"There has only been a handful of these incidents, which we think have been inspired by a trend in America, but we are keen to stop them before they cause anyone else further distress."
There have been reports across the US of men dressed up as clowns trying to lure children into woods, as well as running around with knives and guns.
This has led to a number of arrests as well as police telling people to take photos of any clowns they see to help identify them.