DALLAS – Six people were killed when a pair of World War II-era planes collided in mid-air at a show in Dallas and crashed to the ground in a ball of fire, county authorities said on Sunday.

“According to our Dallas County Medical Examiner, there are a total of six fatalities from yesterday’s Wings Over Dallas air show incident,” Dallas County Judge Clay Jenkins said on Twitter.

Saturday’s tragedy, under investigation by federal agencies, involved a single-pilot Bell P-63 Kingcobra crashing into a larger Boeing B-17 Flying Fortress.

Allied Pilots Association, the collective bargaining agent for American Airlines, confirmed two of its retired members died in the Texas accident.

“Our hearts go out to their families, friends, and colleagues past and present,” the group said on Saturday in a statement on Twitter.

The Wings Over Dallas air show at Dallas Executive Airport was meant to educate people about World War II history and honour the contributions of veterans.

Dallas Mayor Eric Johnson called the incident “a terrible tragedy”. He said on Twitter that “no spectators or others on the ground were reported injured”.

Mr Hank Coates, the chief executive of the Commemorative Air Force (CAF) whose planes were involved in the accident, said the B-17 “normally has a crew of four or five”, while the P-63 is operated by a single pilot.

He said the Sunday part of the air show was cancelled.

Multiple videos posted on social media showed dramatic scenes of the smaller plane descending towards the lower-flying B-17 and crashing into it.

After the collision, the planes appeared to break apart into several large pieces before crashing to the ground and exploding in a ball of fire, creating a huge plume of black smoke.

The crash scattered debris across the airport grounds as well as on a nearby highway and strip mall, Mr Johnson said.

The FAA said its agents and the National Transportation Safety Board (NTSB) would investigate the incident.

Mr Coates said the pilots who operate the planes during such shows are experienced volunteers with “very thorough training” and are often retired military pilots.

He said a mid-air collision at an air show is “extremely rare”. 

The CAF has some 180 vintage aircraft that fly roughly 6,500 hours per year in air shows, tributes to veterans, and training flights, according to Mr Coates.

The B-17, a four-engined bomber, played a major role in winning the air war against Germany in World War II. With a workhorse reputation, it became one of the most produced bombers ever.

The P-63 Kingcobra was a fighter aircraft developed during the same war by Bell Aircraft, but it was used in combat only by the Soviet Air Force.

Mr Christopher Kratovil, a lawyer in Dallas, took his 12-year-old daughter, Kelsey, a history buff like himself, to the air show on Saturday.

He said his father used to take him to air shows when he was a child.

He added that there were several aircraft flying at the same time, perhaps about eight, a mix of bombers like the Flying Fortress and fighters like the Kingcobra. The event included a narrator describing the significance of the aircraft, with patriotic music playing in the background.

Mr Kratovil said the Flying Fortress appeared to be doing a flyby near the crowd, a common move meant for attendees to get a good look.

Then he saw the explosion. His first thought was it could be pyrotechnics, but he quickly realised there was no way to do mid-air pyrotechnics.

He then saw a wing come off the B-17 and then the fuselage of the plane fall to the ground, followed by fireballs and a loud crash.

“It hit me all of a sudden: This is real. You’re watching a B-17 crash,” he said.

“It was just a horrific thing to see and a horrific thing to witness with one of my children.”

One of the last major crashes of a B-17 was on Oct 2, 2019. Seven people were killed after a Flying Fortress that took off from Bradley International Airport, near Hartford, Connecticut, crashed into a de-icing facility shortly after take-off, according to the NTSB.

The agency found that pilot error and inadequate maintenance contributed to the crash.

Mr Paul Martin, a member of the Army Air Forces Historical Association, said he was aware of only about nine B-17s in flying condition and only one P-63 Kingcobra – before Saturday’s crash.

“It’s heartbreaking for me to hear this, both on a human level and a historical level,” he said.

He watched videos online over and over again and still struggled to make sense of the crash.

“To see that Kingcobra fly into the B-17 is mind-boggling to me,” he said. “How do you miss it?” AFP, NYTIMES