MIAMI (AFP) - Maybe it's better to leave the clown costume in the closet this Halloween.

Hysteria sweeping the United States after a series of "creepy clown" sightings in recent weeks has created an unwelcome scare this Oct 31 when Americans will celebrate all things ghoulish, sinister and fantastical.

The Halloween holiday sees millions of American children don costumes and go house-to-house trick-or-treating in neighborhoods across the country.

But cities and law enforcement are discouraging or even banning clown costumes this year after sightings of sinister clowns, some armed with knives.

Authorities fear the bizarre trend could provoke a nasty backlash when children turn out Monday (Oct 31) night.

The unusual sightings began in August with reports of people in South Carolina dressed as clowns trying to lure children into the woods.

The appearances soon spread with more than 20 states now having reported clown incidents, and although most were pranks in bad taste or unverified threats, some arrests have been made, including for attacks.

The craze has even spread beyond the United States to Europe, South America and Australia.

The hysteria has had surprising repercussions for many, such as Armando Santana, a 22-year-old actor who performs as a scary clown in a popular Miami horror house.

He says he would no longer dream of leaving his job without ditching the costume.

"It means that by the end of the night I have to wash my face. I can't drive my car with this on, just in case I get stopped," he said, emitting a classic menacing chuckle.

Even a building in Miami Beach warned its residents ahead of the Halloween door-knocking: "You must be extra careful with anyone wearing clown masks."

Burger chain McDonald's meanwhile has scaled back public appearances of its famous smiley-faced clown mascot Ronald McDonald, citing "the current climate around clown sightings." And discount retail chain Target halted the sale of clown masks because of "the current environment," said spokesman Joshua Thomas.

While some observers have made light of the sightings, police and other authorities are taking the craze seriously.

"Did you know that you could be arrested for wearing a clown mask with the intent to disturb the peace?" warned the Palm Beach County Sheriff's Office on Twitter this month.

The Miami police released a video that shows a boy, fleeing a shadowy clown in the dark, being run over by a car. "These pranks can have serious or even tragic ends," it concludes.

Miami police spokeswoman Yelitza Cedano Hernandez told AFP that, while it is not prohibited to dress like a clown, "if this prank leaves someone injured, the prankster is going to be arrested and the victim's family can take the person to court."

In Kemper County, Mississippi, clown gear has been expressly banned until after Halloween, and authorities will slap a US$150 (S$209) fine on any violators.

Meanwhile a number of US school districts - particularly in New Jersey, Connecticut and Colorado - have banned clown costumes in Halloween parades.

The same action was taken by the city of Belmont, North Carolina, for its Belmont Boo Festival last week: No adult clown costumes allowed.

"People dressed as horror clowns are not 'real clowns,'" said Randy Christensen, president of the World Clown Association.

"They are taking something innocent and wholesome and perverting it to create fear in their audience," he said in a statement.

But some benefit when there's a buzz.

Staff at the Halloween Megastore in Miami said that clown masks, along with superheroes from the film "Suicide Squad" and the US presidential candidates, are hot sellers this season.

And Nelson Albareda, producer of the House of Horror Haunted Carnival in Miami, which has an entire section dedicated to sinister clowns, welcomes the phenomenon.

"I've been in the Halloween industry for 16 years and a lot of people have a phobia on clowns, so this is nothing new to us," he told AFP, while walking the haunted house's dusty passageways.

"Now there's a lot of hoopla about clowns, even on social media. It's actually better for us."