Police warned on Tuesday that "swatting" calls aren't harmless pranks after five Toronto-area schools were forced to activate emergency plans, sparking panic among students and parents.

Gordon Graydon Senior Public School in Brampton, Ont., was placed in a temporary lockdown this morning after police received a threatening call at approximately 8:15 a.m. Police say an unidentified caller told them they had "armed themselves with weapons" and intended to "harm people." The alleged threat also placed four nearby schools in a temporary hold-and-secure mode.

Minutes after the call, heavily armed tactical officers descended on Gordon Graydon. Not many students were inside at the time as the school day hadn't yet begun. Buses heading to the schools were also redirected to the parking lot of a local mall, where hundreds of students waited for hours while officers searched inside and around the buildings.

Some students, however, were already inside Gordon Graydon when police swarmed the building. Daniel Gardner, 12, was getting some extracurricular math instruction when he was told to hide under a table.

"The teacher said they don’t know what's going on -- just (to) stay quiet and go under the table," Gardner told CTV Toronto on Tuesday after the lockdown was lifted.

Police didn't find anything suspicious, and shortly after 11 a.m., police determined the threat appears to have been a hoax.

"Nobody was found -- an area was searched and nobody showed up. Nobody was discovered," Peel Regional Police Const. Lily Fitzpatrick told reporters.

She said officers believe the incident was a case of "swatting," a term for a prank where someone calls authorities pretending to be in danger, and gives an address of an unsuspecting person's home. In this case, the school was targeted, rather than a residence.

The trend originated in the U.S. where celebrities, including Ashton Kutcher, Taylor Swift and Miley Cyrus, have been victims of similar pranks.

"These calls are designed to generate the most massive EMS response possible," Fitzpatrick said. "We believe that that is what the case is here."

She also told The Canadian Press that these types of calls are "not a joke" and waste police resources.

"This is a huge amount of police resources that are deployed to an area because public safety is our number one concern. Somebody who does this, they're not a hero, they're not funny, they've got nothing to be proud of."

Fitzpatrick said officers may release the recording of the initial call to authorities in effort to identify the person responsible.

"There is absolutely nothing that is funny about this sort of thing. It is a serious criminal matter."

There have been a number of recent "swatting" incidents in Ontario.

Over the weekend, police north of Toronto responded to a call after an unidentified man said his father had shot a family member. But when police broke down the door of the Richmond Hill, Ont., home, police found two adults and their children who were shocked to see the officers.

Meanwhile, police in the Niagara Region are also investigating a potential "swatting" call after a mall was evacuated Tuesday morning. Police said a man later called back, telling them the incident was a hoax.

With a files from CTV Toronto's Janice Golding and The Canadian Press