A $100,000 reward is being offered for information that leads to the conviction of anyone who contaminates strawberries with sewing needles in Western Australia, where the number of reported cases is mounting.

The national scare has spread to WA over the past two days, with police informed of five cases, but not all have been verified.

On Tuesday, police said they had received reports of contamination from the Perth suburbs of Kelmscott, Spearwood and Bull Creek, and then a primary school student bit into a strawberry and discovered a needle in Willetton.

In addition, a man in York in regional WA reported finding a needle in his sink after washing locally grown and packaged strawberries on Monday.

WA Police said those responsible could face a charge of acts or omission causing bodily harm or danger, adding anyone who makes false reports could also be charged.

Premier Mark McGowan described the offenders as dropkicks, who were liable to up to 20 years imprisonment.

"You're actually risking someone's life by doing this," he told reporters.

"It's evil. Those people deserve to go to jail."

Strawberry Association WA vice president Paul Da Silva said the contamination was definitely not happening at farm level and looked like "copycats".

"A lot of growers are under extreme pressure at the moment. Some of them are sitting back waiting, actually not picking," he said.

Mr Da Silva said it was "devastating" some strawberry farmers were dumping tonnes of berries due to a price plunge.

Many had ordered metal detectors and he said he would ask Mr McGowan to provide financial assistance to them for the expensive machines.

At Perth's Canning Vale markets, AllStates Fruit and Vegetable Merchants has installed a metal detector to scan strawberry punnets.

But anything can happen at the store level, spokesman Le Bach said, so the company is considering introducing improved packaging.