The pilot lost control of the two-seater and crashed into a wooded area abutting Stewart International Airport in New Windsor, a community about 70 miles north of New York City.
Capt. Brendan Casey with New York State Police said that the pilot appeared to be climbing when something happened to the back of his Giles G202 aircraft and it went into a "steep dive" at about 2 p.m.
"It appears the rear part of the plane broke off," said Casey, who added that there was no distress call.
Ben Granucci, an associate editor with the New York City aviation enthusiasts' website NYCAviation.com, told CNN that the pilot was on his third or fourth run when "he pulled up ... went into a corkscrew and lost a lot of speed."
"A moment later, the plane turned and started crossing the crowd line," said Granucci, who saw the plane's tail fall off. "I knew that wasn't right."
No one on the ground was injured, as the aircraft crashed in a forested area far from people or buildings -- though some did see it happen, including at least one who shared video with authorities.
Authorities did not immediately know what caused the pilot to lose control, with Casey speculating it was due to "a structural failure" but leaving the final analysis to National Transportation Safety Board Investigators.
"I just think this was a tragic accident where it was some type of equipment failure ... that led to this," said Casey, who is the state police incident commander for the air show. "I don't know if there's anything from a safety standpoint that could have been done to prevent this."
Pilot praised for steering clear of people
Despite the fatal accident, Casey said that the New York Air Show -- would go on as scheduled.
The two-day event is set to feature numerous aircraft, including the U.S. military's F-22 Raptor, F/A18E Super Hornet, the AV-8B Harrier and a jump by the parachute team from the U.S. Military Academy in West Point, New York.
The pilot involved in Friday's crash was supposed to be part of the show.
Authorities did not immediately name him, though Casey did say he was a civilian associated with a company involved in air shows.
"He's not from this area," the police captain told reporters, "and we have not been able to notify next of kin."
Granucci praised the pilot, whom he felt looked like he was using "every bit of energy" to get the plane as far away from people as possible.
"He knew that he wasn't going to be landing -- at least not controlled," Granucci said. "I can't even ponder what was going through his had at that point, but if that's the last thing he did, that's commendable and very respectable."
Follows deadly air show crash in England
Last Saturday, a Cold War-era military jet that was part of a southeastern England air show crashed
into a busy highway, killing at least 11 people, British police said.
All of those dead had been on the A27 highway; the pilot was pulled from the wreckage and flown to a nearby hospital, Sussex police Superintendent Jane Derrick said.
The Hawker Hunter aircraft was flying a loop at the Shoreham Airshow -- an event put on the Royal Air Forces Association featuring vintage military aircraft -- when it nosedived.
Earlier this month, a member of the Army Golden Knights parachute team died
after being injured during a performance at the Chicago Air and Water Show, authorities said.
In September 2011 in Reno, Nevada, a P-51 Mustang slammed into the box seat area
in front of the grandstand at the National Championship Air Races.
Eleven people -- including the plane's 74-year-old pilot, Jimmy Leeward -- died.