Four needles have been found with strawberries in Western Australia, with reports mainly coming from the metropolitan area, police say.

A metal detector has been installed at a fruit wholesaler in Western Australia after strawberries contaminated with needles were reported four times over the past two days.

On Tuesday, police said they had received reports of needles being discovered with strawberries in the Perth suburbs of Kelmscott, Spearwood and Bull Creek.

It comes after a man informed the York Police Station in regional WA on Monday that he found a needle in his sink after washing locally grown and packaged strawberries, and did not recall it being there beforehand.

AllStates Fruit and Vegetable Merchants at Canning Vale markets has put in the metal detector in response to the contamination scare.

The pallets are being labelled "scanned for metal contaminants" in a bid to restore confidence in strawberries from the warehouse.

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

The cost of the machines ranged from $30,000 to $50,000, he said.

The WA Strawberry Growers' Association has called on the federal and state governments to provide financial assistance, including a reward for information leading to the culprits being found, much like the one offered in Queensland.

South Australia Police confirmed on Monday two cases of suspected contamination in WA-grown strawberries.

A seven-year-old Adelaide girl bit into a needle in a strawberry from a Mal's Black Label punnet purchased on Saturday from a Littlehampton supermarket.

Later, a second person bought a punnet of the same brand from a fruiterer in Morphett Vale and found a metal object embedded in one of the berries.

Neither person was injured.