Police across England have been called to dozens of incidents in which pranksters dress as "creepy clowns" to deliberately scare people.
Fancy dress shops have been asked not to sell clown costumes to anyone they think might be a prankster amid the ongoing "killer clown" craze.
Forces across the UK have warned that jokers or criminals using the costumes to scare innocent members of the public will face arrest - as they deal with a wave of reports.
The culprits are said to be following a trend that started in the USA.
A teenager from South Yorkshire suffered serious head wounds after a branch was thrown at him by a clown trying to terrorise people in Dinnington. His family posted a photograph to Facebook of bandages covering the sixth form student's head and blood clearly visible.
In a separate incident, a father-of-one claimed he had been left permanently disabled after his fingers were sliced by a knife-wielding clown who crept up behind him at a service station.
The 28-year-old found himself covered in blood as the ten-inch blade cut his right hand 'down to the bone'. He told of the scary moment he was confronted by the clown just after he had withdrawn money from a cash machine, saying it was 'like something out of a horror movie'.
He claims that he grabbed the knife to stop the clown doing any serious harm to his body - but says his fingers 'exploded' following the struggle.
The man was taken to hospital for doctors to try and repair the damage but he says he is now classed as disabled and has been forced to give up his job as a joiner.
Professor Mark Griffiths, a chartered psychologist at Nottingham Trent University, says clowns tend to be scary because of their exaggerated looks and evil representation in films.
"The vast majority of people are not scared of clowns day-to-day but a clown's face has become part of a scare culture.
"There is a stereotype of the nasty, evil, eerie clown. If you look at clowns facially what you tend to find is part of their face or feet are exaggerated, they have huge noses, scary mouths and wildfire hair.
"We also have a cinematic trope. If you look at everything from Heath Ledger in Batman to Stephen King's It, we've got these characters with clown faces that are either killing people or doing really nasty things. Even if you have not come into contact with clowns, you're influenced by what you see in television and films."
Meanwhile, in Kidlington, Oxfordshire, a man dressed as a clown and carrying a baseball bat was reported to have chased a 10-year-old child through a park.