Police responded to a call about the crash at 1.10pm local time. They attended the scene, alongside emergency rescue crews.
Two people in the helicopter at the time have been taken to hospital.
They are in a “stable condition”, police confirmed.
The incident took place near 10th Street, authorities added.
The area from 9th to 11th Street has been cordoned off.
Miami Beach police tweeted: “This afternoon at 1:10 p.m., MBPD received a call of a helicopter crash in the ocean near 10 Street.
“Police and @MiamiBeachFire responded to the scene along with several partner agencies.
“Two occupants have been transported to Jackson Memorial Hospital in stable condition.”
They added: “The beach area between 9 to 11 Street is currently closed.
“The FAA is responding to the scene.”
The helicopter is believed to have been carrying three people.
A statement from the Federal Aviation Authority (FAA) said the helicopter was a Robinson R44.
The crash happened in “unknown circumstances”, they added.
Twitter user @StanthemanAVFC wrote: “I’m sittin on south beach Miami… a f****** helicopter has just crashed into the sea in front of us…”
Another, @QiaGaby, posted: “We are sitting on Miami Beach and a helicopter literally crashed into the sea right infront us where people were bathing.”
She added: “I’m still shaken up.”
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