The piercing of supermarket strawberries with sewing needles is comparable to terrorism, Australia's prime minister said today, as he demanded sentences of up to 15 years in response to a nationwide scare.

Urging Australians to make a strawberry pavlova this weekend to help struggling farmers, Scott Morrison demanded a change in the law to toughen sentences.

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Australia strawberry industry in crisis

"We're not mucking about" said Morrison, after pieces of fruit were found to be contaminated with needles or pins. "This is not on, this is just not on in this country," he said.

Calling the perpetrator a "coward and a grub", Morrison called on parliament to quickly raise the maximum sentence for such deliberate food contamination from ten to 15 years behind bars.

That, he said, would put the crime on par with "things like possessing child pornography and financing terrorism. That's how seriously I take this."

The scare has prompted a series of supermarket recalls, and some stores in New Zealand have temporarily banned the sale of Australian strawberries.

Farmers have been forced to pulp fruit and lay off pickers because of slower sales and lower wholesale prices.

"Just go back to buying strawberries like you used to and take the precautions that you should," Morrison told Australians in a televised address.

"Make a pav this weekend and put strawberries on it," he suggested, later adding in a video message that his wife Jen would actually be doing the baking in their house.

Authorities have suggested strawberries be cut up before they are eaten.

Police on Tuesday said they still did not know the motive for the attacks and were still looking for suspects.

They have asked the public for help with their investigation and are expected later Wednesday to increase a reward for information that helps resolve the case.

The authorities have also complained that the vast majority of the 100 reported cases were hoaxes, and warned that pranksters posting images on Facebook claiming that they have discovered tainted fruit could also face prosecution and potential jail time.

Police in New South Wales said a "young person" has admitted putting needles in strawberries as a copycat prank and will be dealt with under the youth cautioning system.