A vintage World War II-era fighter plane plunged into the grandstands during a popular annual air show near Reno, Nevada, killing three people, injuring 56 spectators and creating a horrific scene strewn with body parts and smoking debris.
The plane spiralled suddenly out of control and appeared to disintegrate upon impact at the National Championship Air Races in Reno, Nevada, at about 4.30pm local time (12.30am today BST).
Bodies were spread across the area as people tended to the victims and ambulances rushed to the scene.
Maureen Higgins of Alabama, who has been coming to the show for 16 years, said the pilot was on his third lap when he lost control.
She was sitting about 30 yards away from the crash and watched in horror as the man in front of her started bleeding after a piece of debris hit him in the head.
"I saw body parts and gore like you wouldn't believe it. I'm talking an arm, a leg," she said.
Among the dead was pilot Jimmy Leeward, 80, of Ocala, Florida, who flew the P-51 Mustang named the Galloping Ghost, according to Mike Houghton, president and chief executive of Reno Air Races.
Renown Medical Centre spokeswoman Kathy Carter said two others died.
Stephanie Kruse, a spokeswoman for the Regional Emergency Medical Service Authority, said emergency crews took a total of 56 injury victims to three hospitals. She said they also observed a number of people being transported by private vehicle, which they were not including in their count.
Ms Kruse said of the total 56, at the time of transport, 15 were considered in a critical condition, 13 were serious condition with potentially life-threatening injuries and 28 were non-serious or non-life threatening.
"This is a very large incident, probably one of the largest this community has seen in decades," she said.
"The community is pulling together to try to deal with the scope of it. The hospitals have certainly geared up and staffed up to deal with it."
The P-51 Mustang crashed into a box-seat area in front of the grandstand, race spokesman Mike Draper said. Mr Houghton said Mr Leeward appeared to have "lost control of the aircraft".
KRNV-TV weatherman Jeff Martinez, who was just outside the air race grounds at the time, said the plane veered to the right and then "it just augured straight into the ground".
"You saw pieces and parts going everywhere," he said. "Everyone is in disbelief."
Tanya Breining, of Hayward, California, told KTVU-TV in San Francisco: "It was absolute carnage ... It looked like more than a bomb exploded."
Ronald Sargis said he was sitting in the box seat area near the finish line.
"We could see the plane coming around the far turn - it was in trouble," he told KCRA-TV in Sacramento. "About six or seven boxes down from us, it impacted into the front row."
He said the pilot appeared to do all he could to avoid crashing into the crowd. After the crash he went up a few rows into the grandstand to view the downed plane.
"It appeared to be just pulverised," he said.
Mr 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 Cloud Dancer.
In an interview with the Ocala Star-Banner last year, he described how he had flown 250 types of planes and has a particular fondness for the P-51, which came into the war relatively late and was used as a long-range bomber escort over Europe. Among the famous pilots of the hot new fighter was wartime double ace Chuck Yeager.
"They're more fun. More speed, more challenge. Speed, speed and more speed," Mr Leeward said.
Mr Houghton described Mr Leeward as "a good friend. Everybody knows him. It's a tight knit family. He's been here for a long, long time," he said.
The National Championship Air Races draws thousands of people every year in September to watch various military and civilian planes race.
They also have attracted scrutiny in the past over safety concerns, including four pilots killed in 2007 and 2008. It was such a concern that local school chiefs once considered whether they should not allow student field trips at the event.
The competition is like a car race in the sky, with planes flying wingtip-to-wingtip as low as 50ft off the sagebrush at speeds sometimes surpassing 500mph. Pilots follow an oval path around pylons, with distances and speeds depending on the class of aircraft.
Nevada Democratic senator Harry Reid said he was "deeply saddened" at the crash.
"My thoughts are with the families of those who have lost their lives and with those who were wounded in this horrific tragedy," he said.
"I am so grateful to our first responders for their swift action and will continue to monitor this situation as it develops."