Mr Hyndman said the school was evacuated immediately, and police were called.
Initially the students and staff congregated on the school grounds, and when deemed safe they moved to the adjacent Sydenham Reserve, he said.
Mr Hyndman said police conducted a search but no bomb was found.
Due to caller ID, a telephone number had been passed to police but it was understood to belong to a telephone exchange based in Wellington, he said.
Mr Hyndman said the all-clear was given by police about 2.35pm, about 10 minutes before school finished for the day.
By that time there were only about 50 to 60 students still at the school as parents who were alerted through a Facebook post were encouraged to collect their children, he said.
Initially the bomb threat was kept from students but after the all-clear was given, he sat the children down and explained why the school was placed in lockdown.
It's been disconcerting for everyone, particularly parents who naturally would have been concerned for their children's safety, he said.
"It's been hugely frustrating and caused a huge inconvenience to everyone."
Judea Rd couple Geoff and Sharlene Evans were among the parents who turned up to collect their children.
Mr Evans said he became aware of the threat after receiving a phone call from a friend who works at Otumoetai College and immediately headed to the school to pick up 9-year-old son Jack.
He had been told by his friend that the bomb threat was made by someone from overseas.
"It's quite concerning. It's good to see a big police presence at the school which really reassures me," Mr Evans said.
Mrs Evans said: "It's probably a hoax call but you really don't know do you? We often hear of bomb threats in other countries before a real strike, so you can't treat these incidents lightly."
Parent Stacey Snookes said she rushed from work to collect her 6-year-old son Nikolai, after reading about the evacuation on Facebook, and only found out about the bomb threat on arrival.
"I was quite shocked. It's a bit scary. I thought it was probably a hoax but you have to treat these threats seriously, and I'm happy how the school and police dealt with this incident."
Mr Hyndman said police had informed him that the school had followed correct procedures, and he would be having a debrief with police about the incident today.
Police Superintendent Chris Schahill said the calls may have been computer-generated.
"We are very aware of very similar incidents occurring around the world, in particular the United States, UK and recently Australia," he said.
Bomb threats in those countries involved recorded voice messages being directed to schools.
"We're currently investigating whether we are the latest in this long string of incidents."
Mr Schahill said if it was found the calls were from overseas, it made it difficult for New Zealand police to prosecute.
Mr Schahill said the investigation was still at an early stage.
The threats were well managed by local police and school management, he said.
Western Bay of Plenty Principals Association president Dane Robertson said he had never heard of this type of incident happening in New Zealand.
"I hope it's just someone's idea of an absolutely ludicrous prank that nobody finds funny. Obviously it causes stress to the students, the teachers, the principal and to the families of students and the community."
Ministry of Education spokeswoman Katrina Casey said the ministry had contacted the schools involved and offered support.
Additional reporting NZME
Other schools who received bomb threats yesterday:
* Logan Park High School in Dunedin
* Wellington High School
* Tamatea High School in Napier
* Christchurch's Burnside High School
* Central Normal School in Palmerston North
Source: Police
