Police in Denver, Colorado, are telling parents to check the candy kids collect during Halloween to make sure it is not marijuana infused, officials said Thursday.

In the first Halloween with legal marijuana in Colorado, authorities are concerned that "edibles" popular with pot users could be mistaken for chocolates or other treats.

"We are suggesting parents do a candy inspection to make sure that the candy is in its original packaging and not just in a zip lock bag," Sergeant Steve Warneke of the Denver police department told dpa.

Parents should dispose of any goodies in packaging that appears tampered with or altered in any way.

"If there is any doubt, throw it out," Warneke said.

Colorado has had legalized marijuana since January, after state voters passed a referendum to allow recreational use of the drug.

Ahead of Halloween, Denver police partnered with a marijuana store owner to post a YouTube video to raise awareness about the potential risk of trick-or-treaters eating marijuana-laced candy by accident.

Marijuana edibles are usually not made from brand-name candy. The candy, which is bought in bulk by the manufacturer, is sprayed with viscous marijuana hash oil. After the oil dries, there is "no way to tell the difference," Urban Dispensary owner Patrick Johnson said in the video.

"This is our first Halloween in Colorado that marijuana has been decriminalized, not just for medical use but also for recreational use, and we do not know if there will be any problems. We are just trying to get the word out," Warneke said.

He urged anyone with marijuana edibles to store them in a secured place.

Colorado was the first state in the US to issue licenses for legal marijuana retail stores.

Washington state started legal sales of the drug in July. Voters in two more states and the US capital, Washington, will decide similar measures in Tuesday's elections.