Streets in the Whanganui town of Marton were cordoned off and a school was placed into lockdown after a person found what are believed to be explosives on Wednesday afternoon.
Stewart, Morris, and High Streets were cordoned off and the New Zealand Defence Force was called in to assist to destroy the items, a police spokeswoman said.
She said police became aware of the explosives after someone found them at a property before bringing them to the Marton station.
Police said in an update just before 6pm that cordons would be lifted shortly.
Marton School was in lockdown following the threat but it has since been lifted.