Arcadia High School was placed on lockdown Thursday afternoon as authorities investigated what began as a serious threat and turned into an infuriating hoax.
An anonymous phone call reporting a "man with a gun" shutdown the school at 180 Campus Drive in Arcadia just before 3 p.m., police said.
By 5:30 p.m., the lockdown had been lifted and students were escorted by bus to parents and guardians waiting at Arcadia County Park on Santa Anita Avenue, the Arcadia Police Department said in a tweet.
It took some five hours for all students to be released to their guardians.
"Stop, stop. These guys -- they're children," one mother said through tears, adding that the hoax cancelled a much-anticipated open house at the school Thursday night.
After the call came in, students were moved to "appropriate locations inside the school" as officers rushed to the scene, police said.
There were no suspects or suspicious persons seen, police said early into the investigation.
A SWAT team assisted officers and the FBI said it was lending its resources to Arcadia police.
Police said one student was escorted out of the school due to an unrelated medical concern.
Traffic was diverted in the area as the investigation was conducted.
The police department tweeted that traffic in the area was heavy, and suggested parents park on the west side of Arcadia County Park, "Huntington, or ABC streets."
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