A jet fighter flown by the US Navy Blue Angels demonstration team crashed on Saturday in South Carolina eyewitnesses said.
There was no word on the fate of the pilot.
The show in Beaufort, South Carolina was attended by thousands of spectators.
"They were doing maneuvers and generally when the planes loop around they cross the runway and then turn around and basically when they turned around we saw a cloud of black smoke," said Brett Hindshaw, a South African who was visiting Beaufort for the air show.
"We started counting and we saw five aircraft. Four of them landed but the lead pilot circled over the accident sight and then one or two military helicopters took off and went in that direction," he told Reuters by telephone.
"Then all the ambulances and military fire trucks stationed along the runway took off."
Witnesses said one of the six Blue Angels jets disappeared as the planes flew low in close formation behind a grove of trees.
One witness, Fred Yelinek, told CNN the jet went down in a high-density residential area and debris hit at least one house and cars, but there was no sign of injuries to people on the ground. He said there was a "huge fireball" at the crash site.