Children discover grenade
Defence force staff were called to Ngaruawahia on Saturday to detonate a Second World War-era hand grenade discovered by children.
The grenade was found at a house near Ngaruawahia and police were alerted about 3.15pm.
"The potential for a tragic outcome in this case was high," Senior Sergeant Andrew O'Reilly of the Hamilton police said.
New Zealand Defence Force staff dispatched from Auckland detonated the grenade on farmland, however no further details about how it was found were available.
Because the Ngaruawahia area was part of an old military range from the 1940s further discoveries were possible, O'Reilly said.
"People out there need to be aware that there probably is ordnance floating around and if it does get located police need to be called and then we'll call the correct people."
Old military equipment has also previously been discovered in Hamilton.
In 2012 home renovators found a mortar bomb beneath a Willoughby St property.
Neighbours were evacuated and a bomb squad called as a precaution. O'Reilly said any equipment found should be treated as "live and potentially lethal".
"It should not be handled in any manner until it has been made safe by Defence Force personnel ... Just don't touch it. Just leave it where it is, come and get police and let the police deal with it."
Police should be called immediately and people and animals should be moved out of the area.
The trained professionals who respond in these situations are from New Zealand Defence Force's Explosive Ordnance Disposal (EOD) Squadron.
The most recent figures available show the squadron had more than 750 callouts in 2012, including a week where there were nine separate incidents the length of New Zealand.