For the second Friday in a row, the Henderson police station was evacuated through a member of the public bringing in an explosive.
The building was evacuated this afternoon until the bomb squad identified the World War II mortar shell as "inert".
Waitemata police district spokeswoman Beth Bates said a woman brought the 60-millimetre mortar round into the station after buying it two years ago at a garage sale.
She was "highly embarrassed" at the outcome, which included the blockading of several roads around the station.
A World War II practice bomb was brought to the station last Friday, triggering the same response
"Our message is, if you find something like this, leave it where it is and call police," Bates said.