Footage from the scene showed mangled helicopter debris smashed into the side of a home whose walls appeared to be cracked and caving from the impact.
The aircraft, a four-seat Robinson R44, landed in a gated community in Newport Beach, some 45 miles south east of Los Angeles, at around 1:45pm.
The helicopter's occupants were being assessed and transported for treatment, Newport Beach police said.
One of the deceased was a person who was on the ground when the crash occurred.
A helicopter crashed Tuesday afternoon in a residential neighborhood about a mile southeast of John Wayne Airport, authorities said. "It was just this intense loud noise". She ran outside and saw a chaotic and gruesome sight.
She said her house shook when the crash happened. At this time, it's not known whether all of those who were killed were aboard the aircraft or whether any of the home's occupants were injured, fatally or otherwise. National Transportation Safety Board officials are investigating the cause of the crash.
This story is developing and will be updated as more information becomes available.