Image copyright Banks family handout

A 10-year-old boy who died in Miami last month is believed to have overdosed on the powerful opioid fentanyl, officials have said.

Preliminary toxicology reports show Alton Banks had a mix of the painkiller and heroin in his system after he collapsed at a local pool.

Officials said they do not believe the boy was exposed to fentanyl at home but could have ingested it elsewhere.

Alton could become one of the youngest victims of the opioid crisis.

"At this point, we have every reason to believe that their preliminary findings are that it was a mixture of heroin and fentanyl that killed this little boy," said Miami-Dade State Attorney Katherine Fernandez Rundle.

"We don't believe he got it at his home," she added. "It could be as simple as touching it. It could have been a towel at the pool."

Police said Alton could have come into contact with the illegal drug on his walk home in Overtown, a poor, high-crime neighbourhood that the Miami Herald newspaper described as "ground zero" for the city's opioid epidemic.

Alton returned home after the pool on 23 June, when he began vomiting and was later found unconscious. He was taken to hospital where he was pronounced dead.

The Miami-Dade Medical Examiner's Office is still conducting tests and is expected to issue a final report determining how the boy died.

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Ms Fernandez Rundle said she commented on the preliminary findings due to the unusual nature of the boy's death and to solicit tips.

Alton's mother, Shantell Banks, told the newspaper her son was a "fun kid" who loved the NFL Carolina Panthers football team and wanted to be an engineer. She was informed of the preliminary findings last week.

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Of the 853 people in Florida who died from fentanyl or a related strain in the first half of 2016, only nine were under the age of 18, according to state records.

More Florida residents died of opioid abuse in the Miami-Dade county last year than there were homicides, the Miami Herald reported.

Fentanyl is an extremely strong, synthetic painkiller that is prescribed for severe chronic pain and is often used to treat cancer patients.

But more recently the drug, which is considered to be 50 times stronger than heroin, has made headlines amid the country's devastating opioid epidemic.

Drug dealers often sell heroin cut with fentanyl on the streets while police have warned the painkiller is so powerful that even touching it could be toxic.

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However, the American College of Medical Toxicology issued a statement last week saying: "Incidental dermal absorption is unlikely to cause opioid toxicity."

"To date, we have not seen reports of emergency responders developing signs or symptoms consistent with opioid toxicity from incidental contact with opioids," the board wrote.

But two months ago a policeman in Ohio said he accidentally overdosed on fentanyl after a drug arrest.

East Liverpool Police Department's Chris Green said he was exposed to fentanyl while searching the car of two suspected drug dealers.

Mr Green was wearing the required gloves and mask to conduct the search, but later brushed off white powder on his shirt with his bare hand.

Shortly after he passed out and was transported to the hospital.