By Leah Asmelash | CNN

Police in Australia are urging the public to stay alert after a runner found homemade spikes methodically hidden on a popular running trail Monday.

The man was on Alexanders Trail in Lake Macquarie, a city in New South Wales, when he noticed a pile of leaves in the middle of the track.

He found wine corks with nails protruding from them, police said in a statement posted to Facebook. They resembled caltrops, illegal weapons that have at least two sharp points sticking out of a base.

He continued along the trail and found another pile of leaves with more spikes hidden. Further along, he found another.

Police are investigating.

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