At least nine people are dead and more than 50 people were injured after a World War II-era fighter plane plunged into the spectators at an air race in Reno, Nevada.
The death count includes those killed on the tarmac and the pilot.
Officials at the National Championship Air Race said a mechanical failure may have caused the P-51 Mustang Galloping Ghost piloted by Jimmy Leeward to plummet out of the sky Friday afternoon and crash into the viewer grandstands.
Reno Air Races president Mike Houghton said the plane was on course before the accident occurred.
"Speculation has gone on a different number of different areas to what took place. Different people see different things. But there appear to be some air-flight problem with the aircraft that caused it to go out of control," Houghton said.
Leeward, 74, a real estate developer from Ocala, Fla. was killed in the crash.
Houghton described Leeward as "a very experienced and talented and qualified pilot" whose "medical records and everything are up-to-date, spot-on."
At least 56 people were taken to local hospitals, including 15 in critical condition and another 13 were listed in serious condition.
Authorities said it is possible the number of injuries may be even higher because some people left for the hospital in private vehicles.
Connie Camit had just left the grandstand for a refreshment stand with two of her children, 14 and 5, ABC News Radio reported.
"Just as we were standing there, we heard this big crash, turned around and I seen airplane pieces, parts flying everywhere," she said. "We just heard everybody screaming, sirens. It was just chaos, complete chaos."
Eyewitness Gerald Lent was on the scene and described the moments before the crash.
"It pulled straight up and did an upside down roll. It looked like no one was flying the plane. It game straight down toward the grandstand," Lent said.
Republican Sen. Dean Heller flew to Reno after the accident and said he wants to be part of investigations into the safety of the event.
"I do not want to see this event here in northern Nevada come to an end. I think it has history, I think people have enjoyed it over the years," he said. "But how do you get over, how do you get over a tragic event like this? And that's what's going to be decided in the next six months."
Federal investigators arrived at the scene of the crash today. An official cause of the crash has not been determined.
"We extend our deepest condolences to the families and friends of those that lost their lives or were injured in this accident," National Transportation Safety Board member Mark Rosekind said in a taped message.
Air race officials have canceled the rest of remaining events for the weekend.
"The National Championship extends their deepest sympathies and condolences to all of the families involved in today's tragic accident. The Air Races are truly one big family and our thoughts are with all of our aviation family members, immediate and extended," air race officials said in a statement.
ABC News' David Wright, Matt Hosford and Jacob Beckman, ABC News Radio and the Associated Press contributed to this report.