The killer clown craze has led to a deluge of calls to Childline from young people left terrified by the sinister phenomenon sweeping the country.
The charity was contacted 120 times in just one week by children scared by people dressed up in clown costumes.
A quarter of the calls came from children under 11, while more than a third came from terrified youngsters between 12 and 15, the charity said.
Most calls came from young people in Birmingham, Manchester and Nottingham, it reported.
The US- born craze has seen cases of clowns chasing children with weapons such as knives or baseball bats, in some instances specifically targeting schools.
A 10-year-old-boy in Plymouth was threatened by a clown who jumped out of a bush carrying a hammer, while in Workington, Cumbria, a clown brandishing an axe chased an 11-year-old girl.
Children have also been targeted online, including a case in which a 13-year-old boy was arrested after a girl the same age in Kendal received Instagram messages from someone posing as a clown threatening to cut her throat and rape her.
Head of Childline, John Cameron said: "There is a worrying trend at the moment with some individuals, be they older children or adults, deliberately seeking to dress up in a way not to entertain but to behave in a very scary and threatening way.
"That's a conscious behaviour and should not be tolerated. Sometimes people don't understand the impact that can have."
He added that parents should warn their children about the consequences of their actions.
"We need to get parents to say to older children, 'If you decide to dress up like that at Hallowe'en, remember you have a responsibility when you're running around the streets - to have fun but don't be threatening and intimidating'," he said.
The NSPCC urged children to call police if they feel threatened in the street and report and block abusive messages online.
Kent Police saw 59 clown-related incidents between October 7 and 10, Thames Valley Police dealt had 14 reports in 24 hours at the weekend and on Wednesday South Yorkshire Police said it had received 61 reports since September 21, including two of clowns with knives.
Armed officers from Scotland Yard's aviation unit also arrested a suspect wearing a clown mask and carrying a fake gun in Hillingdon, near Heathrow Airport, on Tuesday.