At least six NSW schools received the same pre-recorded telephone message between 10.50am and 11.10am on Friday, advising that there was a bomb on school grounds.

Students were evacuated and police conducted sweeps at Lake Illawarra High School, Ulladulla Public School, Penrith High School, St Monica's Primary School in Richmond, Woolooware High School and Mona Vale Primary School but nothing suspicious was found.

Schools in Melbourne and Phillip Island received similar threatening phone messages. On Friday afternoon, Sydney time, dozens of schools in Hawaii and Delaware were also targeted.

In the past few days, hundreds of schools across Britain, France, the US, Japan, the Netherlands and Guam received co-ordinated threats that forced the evacuation of tens of thousands of students.

Calls were made in quick succession to 18 schools in Britain on Thursday morning, local time. In Massachusetts, police stations, hospitals and supermarkets received the same bomb threat "received via automated call system", local police said.

A group of anonymous hackers called Evacuation Squad claimed responsibility on Twitter for many of the bomb threats. However in an email to Fairfax Media, the group said they were not behind the Australian hoaxes.

 "We have only targeted schools in Europe, Canada, The United States, South Africa, and Japan," said a user who used the name Viktor Olyavich. "We are unsure of who it is [behind the Australian attacks]. It is most likely a 'copycat' incident."

Australian authorities said there was no indication of the group's involvement.

Victorian police said: "We are aware that schools in a number of other states and countries have received similar phone calls in the past 24 hours."

A NSW Police spokesman said: "All we can say at this stage is that an investigation into the matter is now under way."

It is understood counter-terrorism police and federal police are not involved at this stage and information gathered by local police on Friday will be collated in the coming days.

Evacuation Squad had posted bizarre messages on Twitter and underground online forums inviting students to get in touch if they wanted to "get out of school", London's Telegraph reported.

They asked people to use an open-messaging system to order bomb threats, asking for bitcoin payments that varied depending on the target. A school would cost $US5 ($7), a courthouse $10, a major convention or sports event $20. They said they also made un-requested threats "for fun".

The group's Twitter account, which has since been suspended, said they were made up of six internationally based individuals but their email used a Russian domain name.

Rodney McKenzie, assistant principal at Cowes Primary School on Phillip Island, said a receptionist received a "computerised call".

"It was a computerised message, like a robot speaking," Mr McKenzie said. "It said there was a bomb located in the school in a backpack."

NSW schools also reported receiving pre-recorded calls, saying a device was on school grounds.

As students at Woolooware High School were evacuated to Sharkies Leagues Club, they posted selfies to Facebook saying they were OK.

"We're all good," one student said.

"We are okay just evacuated to sharks leagues club. so scary," another student posted.