The foolishness began in South Carolina with frightening, false accounts of clowns attempting to lure children into the woods.
From there, reported sightings of so-called creepy clowns spread to other states and even prompted the White House to weigh in on the frenzy.
Now, with Halloween just weeks away, police agencies throughout California are scrambling to calm public anxiety as costumed hoaxsters frighten residents on the street or terrorize others via social media.
Most recently, authorities in Lancaster warned that men wearing "ugly-looking clown" masks were using a kitchen knife to frighten people and then videotaping their reactions.
"They were not the friendly-type of clown," said Ali Villalobos, a community service officer for the Los Angeles County Sheriff's Department in Lancaster.
The clowns have struck at least three times.
Sheriff's deputies said the suspects are "only trying to scare the victim(s)," adding that it was prank.
"There have been reports of 'scare tactic'-style videos appearing online," the department said Wednesday.
Sheriff's deputies have been searching online for videos but haven't found any showing the Lancaster pranks.
Similar creepy clowns sightings were reported in Modesto, prompting police to issue a stern notice to residents: "If you see anything or anyone suspicious, including individuals dressed as clowns, to avoid contact and report the circumstances to us immediately."
The most troubling episodes, according to police, have involved false threats of mayhem against students.
Earlier this week, online pranksters terrorized schools in Oakland, Fairfield and Sacramento by threatening violence against students and staff.
Fairfield police Sgt. Jeff Osgood said a group calling its members the "ClownGanng" threatened to kill or kidnap people at several schools. Although police said the threats were not credible and were merely copycat pranks, officers were monitoring social media and activities on campus closely.
"These viral posts tend to take on a life of their own," Osgood said.
Fontana police also have received reports of people "dressed as clowns are making threats toward citizens."
"Social media has seen this activity occurring across the country for the past several weeks, and it is believed to be a hoax," the department said Wednesday.
Since the clown sightings started in August in South Carolina, police there have attempted to dispel any rumors that the clowns tried to contact or lure children into the woods. The White House even chimed in on the phenomenon when a reporter asked about the sightings in a briefing Tuesday.
White House Press Secretary Josh Earnest said he didn't know whether the president had been briefed on the episodes, but added that local police agencies likely were taking the reports seriously and "should carefully and thoroughly review any perceived threats to the safety of the community."
Not even horror novelist Stephen King could undo the decades of deep-rooted fear of clowns. King's miniseries "It" famously depicted killer clown "Pennywise," who terrorized children in a small town.
On Monday, the author tweeted, "Hey, guys, time to cool the clown hysteria--most of em are good, cheer up the kiddies, make people laugh."
But the effort didn't appear to help.
Clovis police said Tuesday they cited a 12-year-old student after posting threats regarding "Clovis Killer Clowns."
The incident followed arrests made last week in Fresno. Two 14-year-old girls were arrested in connection with threatening to shoot up schools in Fresno — all while making references to clowns. Police Chief Jerry Dyer said the threats were serious and deemed to be felonies.
"Their future is ruined because of something this stupid," he told reporters. "We take this extremely serious, and quite frankly we are fed up. … We want this to stop immediately."
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