It was the second such scare in days after thousands of students were released from schools in New South Wales and Victoria states last Friday due to phone threats.
There were similar scares at schools in France, Italy and Britain earlier last week.
“There is clearly a pattern of hoax calls designed to cause disruption and attract media attention,” New South Wales police said in a statement.
“There is no evidence these are anything other than hoaxes designed to causing unnecessary disruption and inconvenience.
“The threats appear to come from overseas, with no credible evidence they could be carried out here.”
Police declined to say how many schools in the state were affected but media reports put the figure at eight.
Police in Victoria, where reports said about 20 schools had been evacuated or gone into lockdown after receiving threatening calls, said emergency plans had been enacted as a precaution.
“It appears to be a series of hoax calls similar to last week’s incidents, designed to cause disruption and attract media attention,” they said in a statement.
In Queensland, where 10 schools were reportedly affected, police said investigations were continuing but noted “there is no cause for alarm”.
The threats to the French and British schools last week were claimed by a Twitter account calling itself the Evacuation Squad, with a profile picture of Russian President Vladimir Putin.