Superintendent Chris Scahill has said police are investigating the source of the phone messages sent to six schools around the country that threatened bombings on February 24, 2015.

Police believe bomb threat calls to six schools may have come from overseas, but one principal says it was a local number.

Logan Park High School in Dunedin, Wellington High School in Wellington, Tamatea High School in Napier, Burnside High School in Christchurch, Central Normal School in Palmerston North, and Brookfield School in Tauranga all received threats about 12.30pm on Wednesday.

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SUNLIVE Police officers guarded Brookfield Primary School following a hoax bomb threat on Wednesday.

Police said their investigation had indicated that the origin of the calls may be overseas.

READ MORE: Bomb threats to NZ schools 'very similar' to global robo-hoaxes in US, Australia

However Burnside High School principal Phil Holstein said the bomb threat call received by the school was from a Wellington number.

He said the school had received a "pre-recorded automated voice message".

"We took this threat very seriously and immediately contacted the police."

The school continued its last class of the day as normal, so as not to alarm or stress students, he said.

TRACY HARDY/SUNLIVE Police have responded to hoax bomb threats to at least nine schools during the past two days.

Police earlier said they were aware of very similar incidents occurring overseas in countries such as Australia and the United States.

These involved recorded voice messages being directed towards schools in these countries - similar to what schools had reported in New Zealand, Superintendent Chris Scahill said.

Police would be liaising with law enforcement agencies overseas, he said.

'THE THREAT'

Brookfield School principal Robert Hyndman said the threat was made in a phone call to the school's reception at 12.30pm.

"They said there was a threat and we don't have much time," he said.

His secretary alerted him immediately and the school's emergency evacuation procedures commenced.

"I listened to part of the message...it sounded like a male, almost like it had been from a computer, it didn't sound like a natural voice."

Teachers gathered the school's 213 children during lunchtime and evacuated them to nearby Sydenham field.

"We rang the emergency bell and got down to our emergency evacuation area. Everyone was accounted and when police arrived we took them to the reserve where there is more space for them to run around."

Hyndman said the school used its Facebook page to alert parents and request them to pick up students.

Most had been picked up by the time police gave the all clear to return to the school at 2.30pm, he said: "The kids did really well, showed how resilient they were."

"This is the first time and I hope it will be the last time. It's frustrating and a waste of time."

'NOT WILLING TO GAMBLE WITH THAT'

A bomb threat had been received by Tamatea High School in Napier.

"We got a call at 12.30-12.40pm saying there was a bomb planted at the school," principal Robin Fabish said.

"It was lunch time so we rang the alarms and gathered at the school's muster point."

Once the staff and students were briefed everyone was sent home, and within minutes police arrived to search the school grounds for a bomb.

Nothing was found.

Fabish said staff were in the process of notifying parents to let them know it would be business as usual tomorrow.

"It was highly likely it was a hoax but I'm not willing to gamble with that," Fabish said.

"I'm really pleased with our systems and the way they kicked into place."

He said most kids thought it was a hoax when he told them after the evacuation, but support was available for anyone upset by the incident.

A parent of a Tamatea High School student described what happened: "My daughter was at the school. She was in the toilet the fire alarm went off.

"The teachers said it wasn't a drill and students were asked to run to the field.

"When everyone was there the principal said it wasn't a drill. Someone had text the school saying that there was a bomb at the school.

"They were told the police were there searching the school and everyone was dismissed for the rest of the day."

Roy Sye, Tamatea Intermediate School principal, said unlike their sister school they did not receive a bomb threat.

"There was no bomb threat at Tamatea Intermediate School, a threat was made to the High School. They sent their students home. Tamatea High School advised us and we contacted police for advice.

"Our teachers kept students in class as a precaution. We posted messages on Facebook and the school website to advise our parents that all of our students were safe.

"We organised additional staff to respond to parent phone calls. Teachers were kept up to date.

"We received the all clear from police. This 'all clear' was communicated to teachers, students and our community via Facebook and the school website.

"Students were released at the normal time of 3pm. An email will be sent to all families shortly."

CALLER ID

Wellington High School principal Nigel Hanton said police were called after they received a bomb threat about 12.40pm.

"We received a phone call which said that there was a device on the site.

"We got in touch with the police who advised us on evacuation and the risk of that and the likelihood of it being a hoax call.

"They said that they would follow up and they called back soon after and said there had been other calls so it was probably unnecessary to evacuate."

"Based on that we decided to continue with the rest of the afternoon."

"It was lunchtime so the children were all out of the buildings at the time."

Hanton said evacuating would have meant calling the children inside, making sure all were accounted for before sending them outside again.

"The police did plan to do a investigation of the buildings but given the other calls it was decided that it looked to be a hoax."

The school would be operating as usual tomorrow.

The school had caller ID and had provided information on the call to police.

THREAT SOUNDED VERY JUMBLED

Central Normal School principal Shona Oliver said they received the threat around 12.30pm.

She said it came through as a phone call to their reception and sounded automated and was very jumbled and hard to understand.

After receiving the message she said they called the police and their telephony people to see if they could interpret the message.

"The [police] have been down to visit us.

"We followed our protocols and got in touch with police and we have informed our board of trustees."

The school was not evacuated in this instance but she said they had good systems in place should the need to evacuate ever arise.

Police cars have been outside Logan Park High School in Dunedin. A threat was made against the school in January.

STUDENT SAFETY MAIN CONCERN

The Ministry of Education said parents could be assured of their children's safety.

Deputy secretary of sector enablement and support Katrina Casey said the ministry contacted affected schools and offered support.

Schools responded to the telephone bomb threats according to their individual emergency plans and on advice from police, she said.

"Student safety was the main concern in all areas.

"We'd like to assure parents that they can continue to feel confident in sending their children to school, and that schools have the processes and systems in place to manage any threat to student safety.

"Police are dealing with the actual threats."