Investigators arrested a woman from New Jersey for transporting around 15,000 rainbow fentanyl pills into the city, many of them hidden under Lego blocks.

"These pills are hidden in pretty much anything imaginable. Traffickers are very innovative,” agent Frank A. Tarantino III said.

Federal law enforcement officers said the pills had rainbow colors and resembled candy. 

"This is every parent's worst nightmare,” Tarantino said. "This is deliberate. This is calculated. This is treacherous deception to market rainbow fentanyl like candy."

The city's narcotics prosecutor said this seizure comes as one person dies from an overdose in the five boroughs every three hours.

"Overdose deaths are at a record high and 80% of them are related to fentanyl," special narcotics prosecutor Bridget Brennan said.

Prosecutors say drug cartels in Mexico manufactured these pills stamped to look like oxycodone. These substances are extremely powerful and it only takes a small amount to kill someone.

"The lethality of fentanyl, we are talking two milligrams. That is the amount of fentanyl that can fit on the tip of a pencil. It’s approximately 10 to 20 grains of salt," Tarantino said.

Investigators say 40% of the pills analyzed contain a lethal dose and in a recent 15-week operation, the state seized 500,000 lethal pills in several busts across New York.

With Halloween around the corner, prosecutors urge parents to speak to their children about the dangers of these colorful, deadly pills.

"It is critically important to educate the public on this new form that fentanyl is taking across the country and yes, we know it is here in New York,” Brennan said.