Heather Gowans often throws a tennis ball for her dog at Day's Park and is horrified Peppa could have bitten into one of the sabotaged balls. (FILE PHOTO)

Tennis balls containing razor blades have been found at Day's Park, an off lead dog-exercising area in Hamilton.

The Hamilton City Council has passed the matter on to police and officials hope it's an isolated incident.

So far, there are no suspects.

Animal control leader Peter Crocker said two council staff had found two tennis balls containing razor blades at the Chartwell park and disposed of them straight away.

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"It's a concern on how they arrived there, but we have absolutely no idea who has put them there or anything like that," Crocker said.

"It's probably an isolated incident. We don't really get a lot of this kind of thing happening in Hamilton."

Crocker said the council will increase staff patrols at Day's Park.

"We're going to talk to a lot of dog owners in Day's Park and tell them to contact us if they've seen anything suspicious and make sure their own dogs only play with their own toys.

"There are a lot of children and dogs that go down to that park and we don't want anybody - whether it's a child or an adult or a pet - hurt by picking up a ball."

City Councillor Garry Mallett, who lives beside Day's Park, was appalled to hear that his children and labradoodle may not be safe playing there.

"It leaves you a bit speechless, to be honest. You don't know what on earth would motivate a person to do that," Mallett said.

"Obviously dogs grab tennis balls in their mouths and run around all over the place.

"If the blade comes through there, you're going to have a nasty injury. It's bloody horrible."

Mallett hopes police find the culprit behind the malicious act.

"Just see how [the culprit] enjoys eating a tennis ball with a razor blade in it. See what sorts of heroes they are then."

Kool K9 Dog Training's Facebook page was one of many Hamilton dog pages to post the warning. Its post received over 300 shares in under 24 hours.

Owner Joanne Small has four pet dogs and said Day's Park is probably the most popular Hamilton dog park.

"A lot of people are worried," Small said. "It's hard to fathom when you're a dog lover."

She said it sounded as if someone were targeting dogs.

"It's hard to imagine that anyone could be so anti dogs ... [dogs] see one lying around and they would pick it up."

The Hamilton City Council is urging people to keep a close eye on their dogs and report anything suspicious or dangerous spotted in any park to the council or police.

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