Thirteen schools from around the country received phone calls of a "concerning nature" today.

Calls began about 11.20am today and stopped at midday, Police confirmed.

Police attended each school and worked with their management teams.

A number of schools decided to evacuate but most still continued to open after being cleared by Police.

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The calls received today were similar to calls received previously by 27 schools last month.

At least three of the schools have received calls previously.

Police confirmed the calls were a "synthesised voice, with calls occurring at a similar time and day of the week".

They were currently investigating to establish where the calls from and would continue to work with the Ministry of Education and schools to gather information.

While Police took the threats seriously, no schools were in any danger.

"The safety of students, teachers and schools is our priority."

Similar incidents have occurred in United States, and more recently Australia.

Students and staff at Wellington High School were evacuated after receiving a threatening phone call earlier today.

The school's assistant Trish Tuthill said the college received a call shortly before midday.

It was the second phone call the school had received.

Ms Tuthill said the phone call was "exactly the same as last time".

"It was an automated robotic voice."

She said Police were called and gave the all clear shortly after.

"We then dismissed the students from the evacuation collection point and afternoon classes resumed," she said.

She said the calls were "obviously not pleasant".

Wellington's Hutt Valley High School also received a bomb threat call today.