The San Mateo County Sherriff's Office said a woman's body was found in the Half Moon Bay coast by a commercial fishing boat near the crash site amid a search for victims. She was taken to the San Mateo County Coroner's Office.
"The identity of this female adult is still being determined, but it is thought she is likely associated with the plane crash given she was located in the same location."
The search for survivors continued until about 11 a.m. Monday when the Coast Guard said they suspended their search.
The FAA says the plane was a single-engine Cozy Mark IV.
VIDEO: SKY7 shows a part of the plane that crashed in the waters near Half Moon Bay
SKY7 shows part of plane that crashed in waters near Half Moon Bay
The San Mateo County Sheriff's Office says that the plane took off from the East Bay and was found upside down in the water near Ross Cove.
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A spokesperson for the Coast Guard says crews searched around 28 square miles for nearly six hours by helicopter and by boat.
"It's never easy to make the decision to suspend search efforts, and our deepest sympathies go out to the families involved in this incident," said Ian McGoohan, operations unit controller at the Sector San Francisco Command Center. "We are truly grateful for the efforts of our partners assisting in search efforts."
Parts of the plane's wreckage are still being recovered, including a piece just off of Ross Cove.
Authorities are still working to find out exactly where the plane first departed, saying it came from an East Bay airport. It's also unclear if the pilot was trying to land at Half Moon Bay's Airport.
VIDEO:Father and son rescued from ocean near Pacifica, authorities say
Father and son rescued from ocean near Pacifica, authorities say
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"I ran to my window facing the ocean, and I could see that the plane was turning around, and it was losing altitude," said nearby resident Michelle Weil.
Weil said that while planes in the area are normal, what she heard Sunday was different.
"This one was unusually loud and I looked out the window, and I saw it and it was way lower than normal and it was taking a different flight path," she said.
Neighbors say the plane was far from the airport's flight path.
"It was out of the path of the flight, by the time I heard it, it had to have been, there's no way because planes don't fly over my house and that plane was right by there so I'm pretty sure he was looking for help quick, or she," Diana Fernandez, a Half Moon Bay resident said.
The San Mateo County Sheriff's Office says the call first came in just before seven Sunday night from someone at the Moss Beach Distillery who saw the plane flying erratically and sputtering before losing sight of it over the horizon.
"We heard this motor engine puttering like you hear in the movies when a plane is about to crash and you hear the engine and it came around the corner, it's kind of a biplane, very visible," Melissa Richter, a witness said. "We figured something was wrong because it was so close to the restaurant."
Crews got drones in the air and the Coast Guard quickly got a diver in the water, until they discovered the small plane in the water without passengers around 8:30 p.m.
"The plane was actually upside down in the water and this morning (Monday), with about 30 search and rescue volunteers, emergency services bureau, we're beginning to see some of that wreckage come up onto the coastline," Sgt. Philip Hallworth, a spokesperson for the San Mateo County Sheriff's Office said.
At around midnight, Sgt. Hallworth says their search and rescue team made the decision that they couldn't get out there just yet because of low visibility and high tides and resumed their efforts as early as they could around 5 a.m. Monday morning.
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"What's making some of this more difficult is just the status of the tides, the tides have been really high but there's drones out there, the coast guard's assisting," he said.
Ross Sagun was a commercial air pilot out of SFO for more than 40 years.
"I feel so bad for the families. I could just imagine how I would feel," Sagun said.
Registration for the aircraft involved in this crash shows it was a single-engine Cozy Mark IV, which can be "amateur built."
It's unclear if the people onboard the plane were the registered owners.
"The owner - the builder is responsible for the construction of the aircraft and the maintenance of the air craft and operates under a very loose set of rules. Costs about $20,000 to build plus the engine etc. probably by the time it's done - about $30,000 and holds four people, goes about 200 miles an hour," Sagun said.
Sagun said investigators will be looking at weather conditions, the aircraft and air traffic control recordings.
Among the questions - was there ever a mayday call?
"It could mean that whatever happened, happened in a hurry and what happens in that sort of case is the pilot sometimes wont have time to make a mayday call," Sagun said.
A number of agencies including the FAA and the NTSB are now investigating.
Agencies including the San Mateo Fire Department, San Mateo Police Department, and a California Highway Patrol Helicopter aircrew also assisted with search efforts.