A series of hoax bomb threats led to the evacuation of several schools and learning centres across Victoria and interstate on Friday.
Victoria Police said the phone calls were not linked to terrorism and there was no imminent threats to schools.
Berwick Chase Primary, Berwick Lodge Primary School, Aitken Creek Primary School in Craigieburn and Reservoir High School were among the schools.
Victoria Police spokeswoman Leonie Johnson said the origin of the calls was being investigated.
"We are aware that schools in a number of other states and countries have received similar phone calls in the past 24 hours," she said.
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British media reported bomb threats led to 18 schools being evacuated in Britain on Wednesday, following similar events the day before.
Police there are investigating if the calls were part of a co-ordinated, "false and malicious" hoax that spread to France.
The Telegraph reported a Russian Twitter group calling itself "Evacuators 2K16" appeared to claim responsibility for some of the hoaxes and had invited students to get in touch if they wanted to "get out of school".
It said the Twitter account claiming responsibility was removed earlier this week but the threats had continued.
The Guardian reported the account used a profile picture of Russian President Vladimir Putin and an email with a Russian ".ru" suffix.
It said the account's banner picture showed part of a flag linked to Hezbollah, the Lebanese militant group.
Cowes Primary School on Phillip Island was also evacuated after receiving a threatening call about 11am.
Rodney McKenzie, assistant principal at the school, said a receptionist received a "computerised call".
"[It was] like a robot speaking," Mr McKenzie said.
"It said there was a bomb located in the school in a backpack."
Mr McKenzie said the school's 553 students, including new prep students, were evacuated to the nearby cultural centre.
"Police have inspected the school and there's no perceived threat, but students won't be returning to school today," he said.
Berwick Lodge Primary School principal Henry Grossek said an office staff member had answered the phone at 11.24am and heard a male voice.
"Some of [the hoaxes] were automated, but ours was a real voice," he said.
"He said, 'There is a bomb at your school … you haven't got much time.'"
Mr Grossek described being told about the phone call as "terribly frightening".
"We were frozen in fear for a few seconds," he said.
Mr Grossek and the school's teachers then evacuated 565 students, including 85 prep students at their first day of school.
He said some of the children were "confused and worried", especially the younger ones.
While some parents laughed the event off as a harmless hoax, Mr Grossek said in the world's political climate there was now increased fear in such situations.
"I was speaking to police and we've never had anything of this scale happen before," he said.
"We haven't had co-ordinated bomb threats or copycats to schools all on the one day.
"Given what's happening overseas and in our country, we're on heightened alert these days."
Victorian Education Minister James Merlino said a kindergarten had also received a threatening call.
Mr Merlino said the government was taking the calls seriously. "The safety and wellbeing of our students and staff is always our number one priority," he said.
"All of our schools and kindergartens have emergency management plans and the schools affected by these threats have activated them. The Department is providing support to all of these schools."
The mother of a student at Berwick Chase Primary School said the children had been sent home after the evacuation, but "none were worse for wear".
"I have heard that most of the schools involved received recorded messages of the threat," she said.
Several schools across Sydney were also evacuated after receiving bomb threats understood to have been made between 10.50am and 11.10am.
So there's a bomb threat right now as I type in Reservoir High. Is any of us students scared honestly no, we are treating this as a joke.— Michael J Russo (@Mickster112233) January 29, 2016