Police have found a "large quantity" of fentanyl, other drugs and paraphernalia hidden under a trapdoor at a New York City nursery where a boy died from exposure to the opioid.

Photos released by New York City Police Department show more than a dozen plastic bags filled with brown and white powders.

An investigation is ongoing, police said.

A one-year-old died of a suspected drug overdose at the daycare last Friday.

Nicholas Dominici had been at the Divino Niño nursery for just a week. Fentanyl had been hidden in the nap room under a mat as he slept, police said.

Three other children were admitted to hospital after being exposed to the powerful narcotic at the centre in the Bronx.

An analysis of urine from one of the victims confirmed the presence of the drug.

The nursery's owner, Grei Mendez, 36, and her tenant, Carlisto Acevedo Brito, 41, are facing federal charges of narcotics possession with intent to distribute resulting in death, and conspiracy charges, according to prosecutors.

"We allege the defendants poisoned four babies, and killed one of them, because they were running a drug operation from a daycare centre," Manhattan US Attorney Damien Williams said this week.

Both Ms Mendez and Mr Brito were formally charged by a grand jury earlier on Thursday.

Both suspects have been labelled as flight risks by authorities and are being held without bail. They each face life in prison if convicted.

Police said the volume of drugs recovered could have killed 500,000 people. Investigators are also said to have discovered three presses used to package kilos of drugs.

A lawyer for Ms Mendez said his client denied the charges and was unaware that drugs were being kept in the nursery by Mr Brito, her husband's cousin.

It is unclear whether Mr Brito has a legal representative.

Surveillance footage and phone records show that Ms Mendez called her husband several times after finding the children ill - before she contacted 911. Her husband then arrived and removed several full shopping bags from the nursery, officials said.

Ms Mendez also allegedly deleted approximately 20,000 text messages from her phone before her arrest, according to prosecutors. Authorities were later able to recover them.

Authorities are still searching for her husband, who has been identified in court documents as a co-conspirator. He was caught on camera fleeing the scene after the incident, according to police.

Fentanyl, a synthetic painkiller 50 times more powerful than heroin, has been blamed for a rise in US drug deaths.

In 2010, fewer than 40,000 people died from a drug overdose across the country, and fewer than 10% of those deaths were tied to fentanyl.

By 2021, more than 100,000 people had died annually in drug overdoses, with an estimated 66% of those tied to fentanyl.

Credit: The BBC