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.

Police said the experts will now go and check the mortar after the first detonation.
Depending on the state of its fuse, they will either try to remove it or set up another controlled detonation

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

Police then 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.