Reno police said the nine include the plane's pilot. Officials had previously said three people including the pilot were killed in the crash.
A National Transportation Safety Board spokesman told The Associated Press that a team arrived Saturday from Washington to join regional efforts. The spokesman said it was too early to say what caused the crash, though event organizers believe it may have been a mechanical problem.
Friday afternoon, a P-51 Mustang aircraft suddenly pitched upward, rolled and nose-dived toward the grandstand, right next to a VIP section at the National Championship Air Races at Reno-Stead Airport.
As thousands watched in terror, the World War II-era plane slammed into the tarmac and blew to pieces. It appears that other than the pilot, the injuries and deaths were caused by flying parts of the disintegrating plane - not a direct hit.
Besides the pilot, veteran Hollywood stunt pilot Jimmy Leeward, and the eight others who were killed, more than 50 were also injured amid a horrific scene strewn with smoke and debris. The names of the deceased spectators were not released.
The crash left bloodied bodies spread across the area in its wake. Ambulances rushed to the scene, as people tended to victims the best they could with what they had.
Prior to Friday, 17 people had been killed at the National Championship Air Races since their start in 1964, the Reno Gazette-Journal reported. Two of those incidents involved P-51s.
The newspaper also reported that Friday's crash was the first time spectators were killed or seriously injured.
Planes at the yearly event fly wingtip-to-wingtip as low as 50 feet off the sagebrush at speeds sometimes surpassing 500 mph. Pilots follow an oval path around pylons, with distances and speeds depending on the class of aircraft.
Mike Houghton, president and CEO of Reno Air Races, said there appeared to be a "problem with the aircraft that caused it to go out of control." He did not elaborate.
The rest of the races, which bring in tens of millions of dollars for the local economy, were canceled.
According to ABC News, astronaut Mark Kelly was supposed to perform acrobatics in the air races in Nevada. He was scheduled to fly a P51 Mustang, the same model that crashed but not the same airplane.
Kelly and his twin brother Scott are both accomplished fight pilots and like to fly old airplanes.
The Associated Press contributed to this report.