The death toll rose to nine on Sunday in an air race crash in Reno as investigators determined that several spectators were killed on impact as the 1940s-model plane appeared to lose a piece of its tail before slamming like a missile into a crowded tarmac.

Moments earlier, thousands had arched their necks skyward and watched the planes speed by just a few hundred feet off the ground before some noticed a strange gurgling engine noise from above. Seconds later, the P-51 Mustang dubbed 'The Galloping Ghost' pitched oddly upward, twirled and took an immediate nosedive into a section of white VIP box seats.

The plane, flown by a 74-year-old veteran racer and Hollywood stunt pilot, disintegrated in a ball of dust, debris and bodies as screams of 'Oh my God!' spread through the crowd.

America's National Transportation Safety Board officials were on the scene to determine what caused Jimmy Leeward to lose control of the plane, and they were looking at amateur video clips that appeared to show a small piece of the aircraft falling to the ground before the crash. Witnesses who looked at photos of the part said it appeared to be an 'elevator trim tab', which helps pilots keep control of the aircraft.

Reno police also provided a GPS mapping system to help investigators recreate the crash scene.

"Pictures and video appear to show a piece of the plane was coming off," NTSB spokesman Mark Rosekind said at a news conference.

"A component has been recovered. We have not identified the component or if it even came from the airplane ... We are going to focus on that."

A tour near the site offered to journalists on Saturday evening revealed debris spread in a fan-shape over more than an acre around a crater roughly three-feet deep and as much as eight feet across. Based on the crater's location, it appears the P-51 Mustang went straight down in the first few rows of VIP box seats, or about 65 feet in front of the leading edge of the grandstand.

Among the dead were the pilot and eight spectators. Officials said 69 people were treated at hospitals, including 36 who have been released and 31 who remain there.

Nine were in critical condition late on Saturday.

Despite the large number of dead and injured, witnesses and people familiar with the race say the toll could have been much worse had the plane gone down in the larger crowd area of the stands.

The plane crashed in a section of box seats that was located in front of the grandstand area where most people sat.

"This one could have been much worse if the plane had hit a few rows higher up," said Don Berliner, president of the Society of Air Racing Historians and a former Reno Air Races official. "We could be talking hundreds of deaths."

Some credit the pilot with preventing the crash from being far more deadly by avoiding the grandstand section with a last-minute climb, although it's impossible at this point to know his thinking as he was confronted with the disaster and had just seconds to respond.

One of the things investigators said they'll be looking at is the health of Leeward, the 74-year-old pilot, who friends say was in excellent health.

Witnesses described a horrible scene after the plane struck the crowd and sent up a brown cloud of dust billowing in the wind. When it cleared moments later, motionless bodies lay strewn across the ground, some clumped together, while others stumbled around bloodied and shocked.

"I saw the spinner, the wings, the canopy just coming right at us. It hit directly in front of us, probably 50 to 75 feet," said Ryan Harris, of Round Mountain, Nevada.

"The next thing I saw was a wall of debris going up in the air. That's what I got splashed with. In the wall of debris I noticed there were pieces of flesh."

The crash marked the first time spectators had been killed since the races began 47 years ago in Reno. Twenty pilots including Leeward have died in that time, race officials said.

It is the only air race of its kind in the United States. Planes at the yearly event fly wingtip-to-wingtip as low as 50 feet off the ground at speeds sometimes surpassing 500 mph. Pilots follow an oval path around pylons, with distances and speeds depending on the class of aircraft.

The disaster prompted renewed calls for race organisers to consider ending the event because of the dangers. Officials said they would look at everything as they work to understand what happened.

In Reno, the Mustang that disintegrated into the crowd had minor crashes almost exactly 40 years ago after its engine failed.
According to two websites that track P-51s that are still flying, it made a belly landing away from the Reno airport. The NTSB report on the September 18, 1970, incident says the engine failed during an air race and it crash landed short of the runway.

P-51 historian Dick Phillips said on Saturday the plane had had several new engines since then as well as a new canopy and other modifications.

Leeward, the owner of the Leeward Air Ranch Racing Team, was a well-known racing pilot. His website says he has flown more than 120 races and served as a stunt pilot for numerous movies, including 'Amelia' and 'The Tuskegee Airmen'.

In an interview with the Ocala (Florida) Star-Banner last year, he described how he has flown 250 types of planes and has a particular fondness for the P-51, which came into WW-II relatively late and was used as a long-range bomber escort over Europe.