Victoria Police enacted emergency management plans at the affected schools as a precaution.

Ballarat police attended Black Hill Primary School and students were evacuated following a threat.

A planned reptile display at the school had to be abandoned as the emergency siren sounded, with the handlers leaving their snakes, lizards and even a baby crocodile behind. 

The animals are being stored in fridges to keep them inactive, according to the handler.

In the Wimmera, Horsham Primary School’s 298 campus was also evacuated.

The school asked parents not to panic or collect the students, stating the children are safe.

Camp Hill Primary School in Bendigo has been declared safe and students have returned to class.

The school’s assistant principal addressed the children, telling them there was "nothing to be concerned about, nothing to be worried about" and that someone "silly" had called in a bomb threat.

In Hamilton, George Street Primary School has been evacuated.

At least one school in Portland was under lockdown due to the threat.

Meanwhile, police in Queensland, Tasmania, NSW and the ACT responded to incidents at schools across those states.

Police in both Queensland and Tasmania said they suspected the threatening calls were similar in nature to those that had occurred in February, when automated calls were made to schools Australia-wide and later revealed to be a hoax.

"We are liaising with the Education Department and remind people that making threatening phone calls is a serious criminal offence," a Queensland Police spokesman said. "These incidents will be investigated fully."

In Tasmania, calls of bomb threats were made to three schools around 10am, within the space of five minutes, police said.

After attending the schools and conducting enquiries, Tasmania Police said in a statement that: "no concerns were identified and classes resumed".

In NSW, police said operations were under way at schools across the state, but did not specify whether they were in response to threatening calls. However, it is understood the incidents were of similar nature to those in other states.

Two schools in the ACT received threatening calls, but after being cleared by ACT Policing, students were sent back to class.

Three public schools in South Australia also received bomb threats over the phone. Students were evacuated as police searched the properties, but the children returned after the area was cleared.

West Australian police had not, as of late morning local time, recorded any incidents of threatening calls to schools in the state.

The threats made across Australia coincided with threats to schools throughout New Zealand.

New Zealand Police said in a statement on Thursday morning that they were "responding to calls of a concerning nature directed to a number of schools throughout the country".

 "We understand the fear and concern that these calls cause, however we reiterate that so far we have not established any actual threat to any school." 

New Zealand Police added that Thursday's calls "may be similar to those received earlier this year, which inquiries indicated originated overseas".

In February, a spate of hoax calls sparked evacuations and lockdowns at dozens of schools across Australia, including almost 20 in Victoria. 

At the time, police were investigating whether a hoaxer had hacked into the telecommunication service at select-entry state school Nossal High School, located at Monash University's Berwick campus.

A Russian hacking gang called Evacuation Squad claimed to be responsible for the dozens of threats in Australia, as well as similar ones made in the UK, Hawaii, Paris, Japan, the US and Guam over the course of a few weeks.

It is understood some of the phone calls featured an electronic voice message, however it was not clear whether all schools received an electronic message.

At the time, a spokesman for the group calling himself Viktor Olyavich told Fairfax Media via email that the hackers would carry out more bomb threats in the future.

It is not known whether the Russian group is responsible for the latest round of threats.