A charity working with homeless people in Auckland, New Zealand, has unknowingly distributed sweets filled with a potentially lethal dose of methamphetamines.

The sweets were found in food parcels after they were donated by a member of the public.

Auckland City Mission told reporters on Wednesday that staff had started to contact up to 400 people to track down parcels that could contain the sweets — which were solid blocks of methamphetamine enclosed in colourful wrappers.

Three people were treated in hospital after consuming them, New Zealand authorities said, but were later discharged.

Police have opened a criminal investigation.

The amount of methamphetamine in each sweet was up to 300 times the level someone would usually take and could be lethal, according to the New Zealand Drug Foundation — a drug checking and policy organisation, which first tested the sweets.

New Zealand Drug Foundation spokesman Ben Birks Ang said disguising drugs as innocuous goods was a common cross-border smuggling technique and more of the candies might have been distributed throughout New Zealand.

The sweets had a high street value of 1,000 New Zealand dollars (£472) per sweet, which suggested the donation by an unknown member of the public was accidental rather than a deliberate attack, Mr Birks Ang said.

The “initial perceptions” of police were that the episode was likely an importation scheme gone awry, said Detective Inspector Glenn Baldwin, but the nature and scale of the operation was unknown.

Officers have recovered 16 of the candies, but do not know how many are circulating, he said.

The City Missioner, Helen Robinson, said eight families, including at least one child, had reported consuming the contaminated candies since Tuesday.

The “revolting” taste meant most had immediately spat them out.

Auckland City Mission was alerted to the dangerous sweets on Tuesday by a food bank client who reported “funny-tasting” sweets.

Staff tasted some of the remaining sweets and immediately contacted the authorities.

One staff member was taken to hospital after sampling the sweet, Detective Inspector  Baldwin said, adding that a child and a “young person” were also treated in hospital before being discharged.

The charity’s food bank only accepts donations of commercially produced food in sealed packaging, she said.

The pineapple sweets, stamped with the label of Malaysian brand Rinda, “appeared as such when they were donated”, arriving in a retail-sized bag, she added.

Auckland City Mission was alerted on Tuesday by a food bank client who reported “funny-tasting” sweets. Staff tasted some of the remaining candies and immediately contacted the authorities.

They had been donated sometime in the past six weeks, Ms Robinson said.

It was not clear how many had been distributed in that time and how many were made of methamphetamine.

Some of those who had received the food parcels were clients of the charity’s addiction service and the news that drugs had been distributed had provoked distress.

“To say that we are devastated is an understatement,” Ms Robinson said, adding that the food bank — which distributes parcels five days a week — was closed on Wednesday.

Rinda did not immediately respond to a request for comment by The Associated Press.