Police in Wisconsin are warning parents to check their children's Halloween spoils after a mother told officers she found a nail hidden inside a piece of candy given to her child.

The Wisconsin Rapids Police Department warned families after the unidentified mother told police she found a nail inside a green apple-flavored Frooties candy collected while her child was trick-or-treating in Wood County.

Police shared an image of the partially wrapped Frooties and a thin, 2-centimeter-long nail wrapped with green candy.

"We advise all parents to look over their children's Halloween candy (that) they received while trick-or-treating, and to dispose of any that looks suspicious or has broken or unsealed packaging," the department said.

It was not immediately clear from where the candy came.

"At this time we do not have information that would lead us to a residence or suspect," police said.

The case is one of at least three reports of unsafe candy found on Halloween. Police in Maryland are investigating after parents said on Monday night that they found a needleless syringe in their child's candy.

Police in Ottawa, Ontario, said Tuesday that they found no evidence to support a report of sewing needles found in a child's Halloween candy. Officials earlier warned parents to check Halloween loot, although they added that "tampering of candy is rare."