Experts detonate old mortar bomb found in Auckland backyard

A small but thudding bang has sounded out in an Auckland street after an old mortar was discovered in an Epsom backyard.

Police called out: "Stand by, firing" as specialists began a series of "small controlled detonations" at the Pukenui St home in Epsom to safely dispose of the explosive.

The evacuated residents were told they can return to their homes at 11.30am today after a successful detonation, police said.

Inspector Kerry Watson holding the mortar bomb, which was inert. Photo / Dean Purcell

"The New Zealand Defence Force Explosive Ordnance Disposal (EOD) unit conducted a series of small controlled detonations and have now safely disposed of the item," police said.

"The surrounding roads have now reopened and all cordons have been lifted."

The old mortar bomb was dug up in the home's backyard yesterday evening at around 5.15pm.

Inspector Kerry Watson said one of the residents was gardening when he found what they thought was an explosive device.

The man found the mortar when he struck it with a spade.

The explosive experts were unable to determine whether the device was inert or not.

After making it safe last night, they sandbagged the area around the bomb and laid an explosive device next to it to see if they could trigger an explosion.

Watson said the experts were not able to determine if it was inert without trying to first trigger an explosion.

They were unsure what the device was and where and when it was made, but it appeared to be from overseas.

It was quite common for police to get called to reports of potentially explosive devices in homes and building sites.

Watson said the controlled explosions caused very little damage to the area where the device was found.

The homeowner had done the right thing by immediately calling police for help.

With the experts saying that even they couldn't determine whether the bomb was a danger or not, it was important for ordinary Kiwis to always call in help and not handle the devices themselves.

While the area had been evacuated out of an abundance of caution, Watson said the experts were confident there was minimal risk to the area.

Police on the scene in Epsom, Auckland, where an old mortar shell was dug in a resident's backyard. Photo / Hayden Woodward

Police had evacuated four streets and about 100 people in the surrounding area, local resident Cameron de Lile said.

The EOD experts were unable to remove the mortar last night but made it as safe as possible before finding temporary accommodation for the occupiers of the house.

All other residents were then able to return to their homes.

However, police said they had since returned to the area and reinstated cordons and were "evacuating properties in the area as a precaution to allow the EOD team to dispose of the item safely".

"The process of conducting a series of small controlled detonations is expected to take place between 11am and midday today.

"The sounds from this will potentially be heard in the surrounding area."

Jono Pryor and his dog were among the many residents asked to evacuate in Auckland this evening following the discovery of an old mortar shell in someone's backyard. Photo / Hayden Woodward

Police said the public would also notice an increased police presence while the detonation took place and until the area was deemed safe.

Traffic diversions are in place but it is not expected to disrupt any main roads.

"Police will advise when it is safe for evacuated residents to return to their homes," police said.

Radio host Jono Pryor was earlier among the residents evacuated yesterday, saying he and his dog couldn't get back into their house.

"We were about to start our walk just after six and the police came knocking on the door telling us to evacuate."

He said he sat outside his home for about three hours.