Antioch, Fairfield and Oakland police stepped up patrols on school campuses on Tuesday after people — posing as clowns — made threats against several schools on Twitter.
In one of the more violent warnings, clowns on social media promised to shoot at Dallas Ranch Middle School on Tuesday, prompting Antioch police to rush there. Officers searched the school and surrounding areas, and spoke with administrators. Although the threat was deemed a hoax, police said they are continuing to investigate the post and determine who is responsible for it.
Meanwhile, in a letter posted on the Fairfield-Suisin Unified School District website, Grange Middle School Principal Christine Harrison told the public that police found no “credible threat” to the campus, but that officers would be on hand as a “precautionary measure.”
Fairfield Police Sgt. Jeff Osgood told NBC Bay Area on Tuesday that two school resource officers are on each campus, and that parents shouldn't worry. "Your children are safe," he said.
Fairfield we coming,Grange Middle School and Fairfield High School get ready Tuesday(Oct 4th) At 10:30 am.Happy Clowning hehe— ClownGanng (@ClownGanng1) October 4, 2016
Osgood also urged students interacting with the person behind the now-deleted Twitter handle, “ClownGanng1,” to stop.
"These threats would qualify as terrorist threats under California Penal Code, and that will make them a felony," he said.
One of the tweets, sent at 5:40 p.m. on Monday said: “Fairfield we coming, Grange Middle School and Fairfield High School get ready Tuesday(Oct 4th) At 10:30 am. Happy Clowning hehe.”
On Tuesday evening, Osgood pointed out that it was "well past" 10:30 a.m. and there were still "no signs of clowns."
Someone from the account has tweeted 11 times this month, and has 233 followers. Its profile picture shows a clown in yellow pants clutching balloons in a dark parking lot. However, a search for the account around 5:45 p.m. on Tuesday indicated that it doesn't exist and may have been taken down.
Prior to that move, the author or authors had unleashed several “I’m coming to get you” statements to various schools in the district, including Fairfield High, Rodriguez High and PSA,” referring to the district’s Public Safety Academy. And they tell the recipients to “Be Reday.” The language used is also profane, and sounds like it comes from a teenager.
Fairfield High School senior Miguel Cervantes said on Tuesday that he is scared.
"I don't want some crazy guy to walk into my classroom and do God knows what," he said.
Most threats have been ruled hoaxes, and district officials insist that the school is safe and have sent parents letters to that effect. However, students like Miguel didn't want to take any chances.
"I called my mom and said, 'Mom, I really don't feel safe right now,'" he said.
Similar threats had the Oakland Unified School District also on edge.
The social media messages allude to violence, prompting school officials to seek the help of Oakland police, who have bolstered their presence on campuses and launched an investigation, according to a letter sent to the district's parents. Officials also made a robocall to parents about the clown threats.
“The security of our students and staff is our top priority," Jeff Godown, the school district's police chief, said in the letter. "We will be monitoring the situation closely and providing extra patrols to the schools named in the rumors and all schools in general." He added that he called in the FBI to help.
Meanwhile, the director of the Clown Conservancy at the Circus Center in San Francisco said the creepy clown scare puts an ugly face on a noble professoon.
"It has nothing to do with what we as human cartoons are doing with our careers," said Sara Moore. "Clowns go to hospitals and make people feel better. It's annoying to us as real clowns and makes us sad."
In San Mateo, clowns promised on Instagram that they would be at two high schools, but did not make any outright threats, police said Wednesday. Police are investigating the issue and have bolstered their presence in the San Mateo Union and San Mateo Foster City school districts.
Also on Wednesday, a woman said a man dressed as a clown tried to snatch her 1-year-old daughter while they waited at a Concord bus stop. Police are searching for the suspect, who fled the scene.
The threats-by-tweets in Northern California — which have also targeted a number of schools in Sacramento County — are the latest in clown hysteria sweeping some of the nation, including in Fairfield, Connecticut.
On Monday, police in Philadelphia announced a 13-year-old girl was behind some of the social media posts threatening violent "clown attacks" at her school. And police in New Jersey arrested a 13-year-old girl and 14-year-old boy for allegedly making similar threats.
Most recently, the creepy clowns began appearing in August in South Carolina, when children started telling police that a group of clowns had offered them money to accompany them to their home deep in the forest, NBC News and others have reported.
But Slate has also reported that these clown threats have been a "thing" since 1981, and crop up every few years.
Since the summer, clown sightings have sprung up in about 30 states, leading to arrests, warnings and a flurry of media reports crying hoax or mass hysteria. Each city has a different clown account. In Kentucky, for example, the Twitter handle is @Clownclann.
Halloween is at the end of this month.
NBC Bay Area's Jean Elle contributed to this report.