A supermarket shopper discovered a needle in a strawberry on Thursday after returning home and alerted staff at Woolworths in the Darwin suburb of Nightcliff who told police.
More than 100 reports of contaminated fruit have been made in every state around Australia, with the problem beginning in Queensland earlier this month when needles were found in strawberries, sparking copycats.
NT Police deputy commissioner Grant Nicholls said it was a serious incident and anyone contemplating such "stupid criminal activity" would go to jail following new laws introduced last week.
"I am confident we will get to the bottom of this, there is myriad investigative techniques we can apply, there are a lot of CCTV cameras out there so I think we need to watch this space," he told reporters.
NT Health chief executive Catherine Stoddart said people should chop any fruit up before eating for the time being.
So-called "food terrorists" will face 10 to 15 years behind bars after the government rushed tough new penalties through parliament.
The government passed draft laws on Thursday in under four hours after Prime Minister Scott Morrison announced a crackdown on people sticking needles in strawberries.
Labor called for a review of the changes in 12 months to deal with any unintended consequences, particularly the inclusion of "providing the public with food" in the revised definition of "public infrastructure".
This new definition ties food contamination to national security.
The Queensland and NSW governments are offering a reward to catch the culprits.
The government is also providing $1 million to make more food safety officials available to increase detection, fast-track recalls and help the industry to rebuild confidence.
Supermarket giant Woolworths has taken the extraordinary step of withdrawing sewing needles from its shelves nationally.
