Young possum joeys were taken from their mother's pouch and drowned in a bucket of water during an annual fundraising hunt for a South Auckland school.
Hundreds of adult possums were killed during the event raising money for Drury School last weekend, with a witness telling the Herald on Sunday at least one teenaged girl - not a student of the school - was allegedly involved in the drowning of the baby possums.
The Ministry for Primary Industries confirmed it was investigating the incident and the school has vowed it is changing policies for next year's hunt - which is organised by the parent-run organisation Friends of Drury School - after discussions last week with the SPCA.
Last Sunday's weigh-in - where the drownings occurred - came after several days of possum hunting, with hunters bringing the dead adult marsupials in for weighing, before they are sold to a fur buyer as part of a fundraising initiative.
School board of trustees chairman Emiel Logan said in a statement the hunters were required to remove and humanely dispose of any joeys before the possums were brought to the weigh-in, but some hunters did not.
"Any joeys found dead or alive were removed from the carcass as the fur buyer doesn't take any joeys.
"They were then put down of in a manner that was believed to be lawful."
Logan said no primary or intermediate aged children were involved in the removal or disposal of the joeys, but a number of teenagers were among volunteers who helped run the event.
But he did not respond to questions whether the teens - who do not attend the school - were involved in the culling of the babies.
The SPCA had since been in touch with the school to explain the method of killing the joeys was not considered humane, Logan said.
"The school has learnt from this and we will be working with the SPCA to ensure that all animal welfare requirements are met in future so that the focus is returned to the commendable intent of the fundraising itself."
An MPI spokeswoman confirmed it had received a complaint and were making inquiries to determine if an offence had been committed.
Drowning animals is illegal under the Animal Welfare Act and is punishable by a fine up to $75,000 or a maximum three years' imprisonment.
"MPI will also visit the school to ensure the school or relevant committee is aware of their responsibilities for future events," the spokeswoman said.
"There is guidance available for humanely euthanising young possums and this will be shared with the school.
"MPI is very aware of the need for animal welfare education at schools and has developed resources to support teachers."
The complaint to MPI was made by Lynley Tulloch - an animal rights activist - who attended the event after telling organisers she was an environmentalist from the Waikato and was writing a children's book.
She told the Herald on Sunday she witnessed a teenage girl pulling live joeys out of possum pouches and dropping them into a large bucket.
She was told by those present the girl was drowning the joeys.
Tulloch said the drowning of the joeys was "absolutely appalling".
She added she was "absolutely sickened" by what she saw.
SAFE chief executive Jasmijn de Boo said drowning was an unacceptable way to kill an animal.
Drowning newborn animals is considered particularly cruel because they have an automatic reflex to hold their breaths, meaning it takes longer for them to lose consciousness than if they inhaled water.
"It's not quick and it's causing severe distress."
Schools teaching children to kill animals desensitised them to violence, she said.
Possums were cruelly treated in New Zealand, de Boo said.
"I know they cause damage but they're still sentient beings with feelings."
As well as complaining to MPI, Tulloch has also started a petition to ban school possum hunts.
The petition has so far gathered almost 3000 signatures.