Video shows a helicopter crashing into the water mere yards from a crowded Miami beach

• Two people were injured Saturday after a helicopter crashed at a Miami beach.
• The FAA said the crash occurred "under unknown circumstances" and is investigating the incident.

Two passengers were injured Saturday after a helicopter crashed into the waves close to crowds of beachgoers, local and federal authorities said.

Video posted by the Miami Beach Police Department showed a black helicopter careening through the air just above the shore of a crowded beach dotted with swimmers and sunbathers. The helicopter ultimately crashed into the waves right next to several swimmers.

The Federal Aviation Administration told Insider in a statement that the Robinson R44 helicopter crashed into the Atlantic Ocean "under unknown circumstances" Saturday afternoon.

The agency said three people were aboard the helicopter at the time of the crash and that the FAA and the National Transportation Safety Board are investigating.

Miami Beach police said the two injured helicopter passengers were taken to a nearby hospital and were in stable condition.

One witness who was at the beach, Sean Adams, told CNN affiliate WPLG he saw the helicopter moving "back and forth over the deep water several times" before the crash occurred. He said he saw the pilot exit the helicopter, but that the two passengers appeared "somewhat unconscious" and "in shock" while others helped them out of the wreckage.

"The whole beach ran to the scene," Adams told WPLG. "Probably ten guys pulling the skid down so it didn't collapse, because it was sitting on the blade. When the blade snapped, the helicopter started going over, so while we are pulling the skid down, two guys were inside pulling the passengers out."