A suspicious device found on Hampden Beach sparked a call to the bomb disposal unit on Sunday.
Oamaru police Senior Sergeant Jason McCoy said at about 1.40pm on Sunday, a suspicious parcel with wires sticking out of it was found on Hampden Beach.
Hampden police Constable Darrin Low went to the scene and police made contact with the bomb disposal unit, who were ready to attend until it was discovered that it was a Niwa atmospheric device that had washed ashore.
"They were stood down," Mr McCoy said.
"It turned out to be a Niwa atmospheric device. There were some concerns with the wires sticking out of it."
Police suspect the item had come off a weather balloon and washed in from sea.
The incident has prompted a reminder from police not to touch anything suspicious.
"Just a reminder for people, if they do find something like that, not to pick it up and move it, to call us to come and check it out," Mr McCoy said.
"If you are thinking that it is a bomb, make sure you leave it where it is and contact the police and keep well away from it."
The item will be returned to Niwa.