A plane crash at an air show just outside of Reno, Nev., has caused mass casualties, officials are reporting.

A P-51 Mustang piloted by a Florida real estate developer, Jimmy Leeward, crashed in front of a grandstand at the National Championship Air Races and Air Show on Friday. The accident was caught on video and posted on Youtube.

The Renown Regional Medical Center in Reno reported 21 patients as of 8:45 p.m. EDT and said no more patients were expected, but it did not give the conditions of any of the patients or say how many had died.

Witnesses described a horrific scene. One guy was cut in half, Gerald Lent, a doctor and a Reno resident, told the Reno Gazette-Journal. There's blood everywhere. There's arms and legs. One guy just said, 'Hey, there's another foot over here.'

Another witness, Greg Schwab of Provo, Utah, told USA Today that he thought at least 50 people were injured. I did not see a single person stand up, he said.

Mike Draper, a spokesman for the air show, told CNN that the plane, the Galloping Ghost, had been competing in a qualifying round and crashed around 4:15 p.m. Pacific Time, or 7:15 p.m. EDT. About a lap in, the pilot sent a mayday signal and then crashed into a box seat area.

It was clear that the plane was pulling up and was in distress, Draper told CNN, adding that there was no word yet on what had caused the crash.

One spectator, Ken Wiegand, a civilian pilot, told the Los Angeles Times that he could tell something was wrong before the plane went down.

Being a pilot, you could see trouble as soon as he hit the apex of his pullout, Wiegand said. You could tell he was in trouble and was probably going to crash. It took about five seconds for all of this to happen.

I thought he was coming right on top of us, one witness, Fred Scholz, told CNN. Luckily there was no fire, which surprised me. It just happened so quickly.

Because the accident occurred so suddenly, the spectators beneath the plane had no time to escape. A Federal Aviation Administration spokesman told CNN that there were multiple fatalities and critical injuries.

Leeward, the pilot, who was presumed dead in the crash, had worked as a stunt pilot in several movies, including Tuskegee Airmen and Smokey and the Bandit Part 3. He was 80 years old.