A US company has released a kit that allows parents to test their childrens' Halloween sweets for traces of cannabis amid concerns over edible marijuana.

CB Scientific has created a $15 (£10) kit, which screens sweets for traces of Tetrahydrocannabinol, otherwise known as THC, the psychoactive drug in marijuana.

Derek LeBahn, of the firm, explained how the procedure works to the US news site CBS Denver. Essentially, the equipment works in the same way as a home pregnancy test kit.

To test for THC, a small sample of the food needs to be broken off and placed into a test tube, where a solution and a dye are added. If the product contains the cannabinoid, it changes colour within ten minutes.

When testing a cookie for CBS4, LeBahn said: "See it turn pink? Definitely a positive for THC."

The intensity of the colour depends on the potency of the THC in the food.

According to the company, the test kit can detect the difference between cannabis and fake marijuana. LeBahn added that it can also be used by medical marijuana users to test how potent their products are.

The kits are being sold online and marijuana dispensaries.

With Halloween one week away, Colorado police have warned parents that their children could ingest sweets or other foods laced with cannabis.

"Apples, gummy bears, there's a ton of different edible stuff out there on the market that is infused with marijuana" said Sgt Brett Hinkle, in an official podcast.

Colorado became the first state in the US to legalise marijuana sales for adults for recreational use, followed by Washington. The two states are being monitored closely by others considering whether to decriminalise or legalise the drug.

In November, voters in Alaska and Oregon will vote on whether to also legalise recreational marijuana use.

"They need to look at every single piece of candy," said Jill Boyle, the emergency room director at Saint Anthony's Summit medical centre.

The Frisco-based centre,near Denver recently launched an educational campaign asking parents to be "edible aware."

"Edibles have a large amount of THC in them," Boyle told CBS4. "We don't want our children getting a hold of that and being critically ill."