Boyd Tce flatmates Aidan Milner, left, and James Winstanley have been aware of the shell on their property since they moved in four months ago.

A pair of police officers and an incredibly daring cat at the scene of a bomb scare in Newtown.

Police cordon off part of Adelaide Rd as the bomb shell is detonated at MacAlister Park, Newtown.

A bomb dating from the 1800s found in Wellington's Newtown suburb this morning has been detonated.

The Defence Force Bomb Disposal Unit was called to Boyd Tce, a small road off Adelaide Rd, in Wellington, where the shell was found on a building site at 9.15am today.

It was taken to nearby McAllister Park where it was put in a hole, covered with sand bags, and detonated with a loud bang shortly before 3pm.

ROSS GIBLIN/Fairfax NZ AT THE SCENE: Police officers at the Newtown address.

Earlier today, a tabby cat unwittingly risked its life by playing with the shell, which military bomb experts described as a six pound (2.7 kilogram) ''breech loading shell'' from the 1800s.

The shell was treated as though it was explosive and full of gun powder which does not deteriorate easily over time.

Residents at the property Aiden Milner, 19, and James Winstanley, 19, both Victoria University students, had been aware of the bomb's presence since they moved in four months ago.

Milner said they had looked down at the shell from their deck and were not threatened by it because it had a hole in the top of it.

However, they became aware of the danger when two builders arrived on site this morning to do excavations for work on the deck.

Unlike the students, the two builders ''were out of there'', Milner said.

''We did not think it was dangerous 'til the builders arrived. They were out of there in a hurry and we thought we better report it.''

Military experts were earlier working on keeping the powder dry.

Sergeant Bruce Mackay said the site was thought to be a former military barracks.