Rodney Police Area Commander Inspector Mark Fergus said the man was in police care while his mental health was assessed.
He said the man was not found with a weapon.
It was not yet clear if charges would be laid, said Mr Fergus.
"Police commenced the search as a result of some threats made around local schools," said Mr Fergus.
"The purpose was to find this man who was suffering a mental health crisis."
Mr Fergus would not disclose how the man made the threats.
He also raised concerns with misinformation being circulated on social media, and would not address some of the claims being made.
"Much of it is unfounded," he said.
Whangaparaoa College Acting Principal Robyn Brownlee said students were bundled into the nearest classrooms as soon as police informed them of the threats.
"All staff and students all responded really positively," she said.
She would not confirm if the man at the centre of the incident was a former student or if he was known to the school.
"That's a police matter," she said.
Several other schools in the area went into voluntary lock down.
The mother of a student at the school, who did not want to be named, said it was believed the man was an ex-student with a grudge against the school.
The woman said her son had been "a little worried" and been in touch many times.
"They were locked in the classroom, complete lockdown, there's a heavy police presence around the school and what not," she said.
"He said he heard there was somebody out there the police were looking for with a knife on school grounds."
Other parents collected their children from school early.
