"These fireworks should be banned. They are a ridiculous hazard for lots of animals, not only horses. They get absolutely terrified."
Bay of Islands SPCA animal welfare officer Wendy Locke was alerted to the incident, but the horse had died by the time she arrived.
"There were lots of fireworks for New Year's, and the horse was obviously pretty stressed from the noise of it, and had been galloping around. We aren't sure if she's gone through a fence or what, but it was really not a good [injury].
"It was really sad turning up and seeing the leg like that and this little baby foal cuddled up with Mum," she said.
The foal was dehydrated, but had responded well after taking milk from another mare.
Ms Locke agreed with Mr Harrison that the incident served as a further warning about the danger of fireworks.
"Kaikohe was pretty rife with fireworks [on Tuesday night], over the back of the farm and out the front over the Kaikohe township," she said.
"I don't support the private use and sale of fireworks to the public for reasons like this. All sorts of stock, horses in particular, can become highly stressed."