Mr Stewart did not give details but confirmed police were also investigating a banana contamination.
A police statement released last week said contamination could now affect Donnybrook Berries, Love Berry, Delightful Strawberries and Oasis brands, along with Berry Obsession and Berry Licious, the two brands named earlier this week.
Nervous growers are weighing up their farming futures as the strawberry contamination crisis forces New Zealand's major supermarkets to stop selling the fruit from Australia.
"The Australian authorities have thoroughly tracked export orders for strawberries and can confirm none have been imported by New Zealand", MPI's manager of compliance investigations, Gary Orr, said.
All reported incidents will be investigated thoroughly.
Tasmania Police said they were contacted by a Woolworths at Rosny Park in Hobart on Sunday evening over strawberries allegedly contaminated with a needle being reported on social media.
"New Zealand-grown strawberries will be on our shelves from next week as it's the start of the new season", Steve Sexton, Countdown's head of produce, said.
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A man posted a picture of the needle he found in a strawberry punnet.
"These further instances are cases in which needles have been found within the strawberries and people have gone to eat them, have cut them up and found the needles".
Authorities are hopeful a $100,000 reward for information offered by the Queensland government will lead to the capture of the culprit or culprits.
Officials said it is still safe to buy strawberries but consumers should cut them up before eating them.
Federal Health Minister Greg Hunt has ordered the food safety watchdog to investigate Queensland's handling of the strawberry spiking saga. "It is a very, very broad picture and we can't speculate in any way, shape or form", said Terry Lawrence, Queensland acting chief superintendent.
Growers have expressed concerns that the scare, which has come during the peak of production, could have a negative effect on sales for an industry worth about A$130m a year.