An unexploded military marker has been detonated by defence force personnel on the New South Wales South Coast after it was discovered by a young girl collecting shells.

Bradley Tangye was with his stepdaughter on Bradys Beach, north of Ulladulla Harbour, on Tuesday morning before school when she picked up the unexploded ordnance.

Mr Tagnye said at first he did not know what she had found.

“I wasn’t too sure — it was a cylinder, sort of green, but then I saw it had ‘flammable’ written on it,” he said.

“It had ‘dangerous, may contain phosphorus’ on the label as well.

Mr Tangye phoned the police after reading a message on the explosive advising that the police or military be notified “right away” if it was found.

“They were there within five minutes,” he said.

Police arrived at the beach at about 8:30am to set up an exclusion zone before defence force personnel were brought in to safely detonate the device.

‘The whole place shook’

A post was made on social media warning people about the beach closure while defence worked to detonate the device.

Despite the warning, dozens on people gathered to watch.

There were plenty of reactions to the blast on social media.

“I heard that!” one post said.

“I think the whole town did,” another person responded.

A person posted that they were at a nearby café and that “the whole place shook”.

On its website, the Department of Defence warns people not to touch or disturb suspected unexploded ordnance, because “very little handling may be needed to make the item of ammunition function”.

Defence has been contacted for comment.