"We don't know why dogs like the berries, but dogs are scavengers and will eat anything."
Owners should not let dogs off the lead to roam near karaka trees and they were urged to seek the advice of a vet immediately if they suspected their dog had eaten the berries.
"Get to a vet clinic as fast as you possibly can. Your dog may show signs of nausea and could have diarrhoea and restlessness.
"This quickly progresses to more severe gastrointestinal signs and neurologic signs that include pacing, limb rigidity, crying, seizures then unconsciousness."
Chance of survival was lower once a dog started to have seizures and became unconscious.
Serious cases required specialist 24-hour care, he said.
The lower branches of a Karaka tree. Photo / Supplied