A US police officer's body camera captured the incredible moment he saved a boy's life when the 3-year-old was choking on a coin.

Oklahoma sheriff's deputy William Wheeler saw a woman asking for help at a car wash on June 8 and rushed to her side.

Victoria Terrill had noticed her son Chaz was choking while they were driving back from dinner and immediately pulled into the car wash parking area.

The mother reportedly thought the boy was choking on a lolly so the officer tried to hit the Chaz on the back of the head in the hopes of getting him to spit it out.

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But it turned out the boy was choking on a coin.

After Wheeler hit the boy on the back three times, the coin came flying out of Chaz's mouth.

"You okay, buddy?" the police officer then asked.

The mother says she police officer was "like a guardian angel". "He just happened to be going by at the exact time I needed him."