Cincinnati has become the latest American city to be hit by a huge wave of heroin overdoses in a single night, recording 20 mostly in a three-hour period.

No-one died on Tuesday night and the victims were revived with Narcan, the anti-opiate medication that has become a frontline defence in the war on drugs.

Authorities in the city say they have launched an investigation into whether the overdoses were connected, and whether a contaminated or super-strong consignment of heroin was to blame.

And more overdoses were also reported in southeast Indiana county, about 75 miles from Cincinnati.

Local police issued a warning to drug users to be extra careful.

Lt Steve Saunders: “The Cincinnati Police Department has received preliminary information that there have been a very high number of heroin related overdoses in the area today.

“This has been generalised on the west side of Cincinnati, but it does not mean this compound is not in other areas.”

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One man was revived after passing out in his car with a six-year-old boy in a petrol station car park.

Joyce Alexander, Shell manager, told WLWT TV, she tried to calm the young boy.

“I started crying. I did,” she said.

“I started crying and I asked him questions. I got him calmed down, gave him a toy to play with and he said his mom’s in jail and he lives with his grandma. It’s sad.”

The introduction of Narcan is credited with controlling the number of deaths from opiate overdoses even as abuse of prescription drugs and heroin are on the rise. However, some public health officials fear it has caused an increase in the number of overdoses among addicts who know they can be revived from ever higher drug doses.