Hoax phone calls that have forced the evacuation of dozens of Australian schools are designed to cause nothing more than disruption, police say.

Schools in Queensland, NSW, Victoria, Tasmania and the ACT were evacuated in the latest round of threatening calls on Tuesday.

The anonymous automated calls, apparently from overseas and not terrorism-related, have caused major disruptions for teachers and students in the first days of the school year.

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In some cases, bomb squads have searched school grounds and children have suffered heat stress after being forced out of air-conditioned classrooms and onto school ovals in stifling temperatures.

Police in NSW, Victoria, Queensland and Tasmania considered the threats to be inconvenient rather than credible.

“There is no evidence these are anything other than hoaxes designed to cause unnecessary disruption and inconvenience,” NSW police said on Tuesday, following three consecutive days of evacuations.

Victorian Education Minister James Merlino said the callers were cowards who would be punished when caught.

Nearly 20 schools in Victoria went into lockdown on Tuesday, including some that were targeted on Friday.

In Queensland, 10 schools received threatening phone calls, including Townsville State High where a bomb squad searched for suspect devices.

“We will meticulously search every room, every cupboard,” Senior Sergeant Matt Lyons said, adding it could take days.

Schools in southeast Queensland were evacuated in stifling heat, with a 12-year-old schoolgirl at MacGregor State High, on Brisbane’s southside, taken to hospital suffering heat exhaustion.

Five schools in the ACT and several in Tasmania were also evacuated after receiving the threatening phone calls.

Victoria Police Chief Commissioner Graham Ashton says each call has to be taken on its merits, despite the series of hoaxes.

Because the calls are automated, Mr Ashton says it’s difficult to determine whether an individual or group is behind them.

“Also because of the international nature of this threat, that adds another layer of complexity to the investigation so it may be some time before this investigation properly identifies, and we’re able to arrest, these people,” he said.