A young boy has been arrested after admitting to putting needles in strawberries.

On Wednesday, NSW Acting Assistant Commissioner Stuart Smith said detectives had already arrested one young boy over behaviour that “could be a prank”.

“Obviously in the last few days we found a young person has admitted to a prank, including putting needles in strawberries, and he’ll be dealt with under the youth cautioning system,” the acting assistant commissioner said.

View photos A young boy has been arrested over putting needles in strawberries in a “prank”. Photo: AAP More

In NSW the maximum penalty for deliberately contaminating a food source is 10 years in jail.

Detectives believe all the incidents of fruit contamination in the state have been the work of copycats and pranksters and have vowed offenders will feel the full weight of the law.

Needles have been found in more than 20 punnets of strawberries across NSW in the past week after the fruit was first sabotaged in Queensland.

Woolworths took the extraordinary step on Thursday of removing sewing needles from its store shelves.

In Perth parents were sent letters about sabotaged strawberries at four Perth schools.

Needles have also been discovered in an apple and a banana, NSW Police confirmed on Tuesday.

Prime Minister Scott Morrison on Wednesday announced urgent and harsh new Commonwealth criminal penalties for contaminating food as the ongoing needle crisis brings many Australian farmers to their knees.

“This is a shocking and cowardly thing for this individual and others who have jumped onto the bandwagon here to have engaged in,” Mr Morrison told reporters in Canberra.

He wants the maximum penalty for food contamination increased from 10 to 15 years in prison, in line with child pornography and terror financing offences.

NSW Premier Gladys Berejiklian has promised to stand shoulder to shoulder with farmers.

“It is beyond belief that anybody would deliberately sabotage fruit to try and harm people in the process, harm our hardworking fruit farmers and the industry,” she told parliament.

“This is a disgusting act designed to instil fear in consumers and to undermine our agricultural industry.”

NSW produces around one per cent of Australia’s strawberries. The state’s strawberry picking season is expected to begin in the next six weeks, according to the premier.