DALLAS (AP) — Two historic military planes collided and crashed to the ground Saturday during a Dallas air show, exploding into a ball of flame and sending plumes of black smoke billowing into the sky. It was unclear how many people were on board the aircraft or if anyone on the ground was hurt.

Anthony Montoya saw the two planes collide.

“I just stood there. I was in complete shock and disbelief,” said Montoya, 27, who attended the air show with a friend. “Everybody around was gasping. Everybody was bursting into tears. Everybody was in shock.”

Emergency crews raced to the crash scene at the Dallas Executive Airport, about 10 miles (16 kilometres) from the city’s downtown.

Live TV news footage from the scene showed people setting up orange cones around the crumpled wreckage of the bomber, which was in a grassy area.

“The videos are heartbreaking,” Dallas Mayor Eric Johnson wrote on Twitter, adding that the National Transportation Safety Board had taken control of the crash scene with local police and fire providing support.

The Boeing B-17 Flying Fortress and a Bell P-63 Kingcobra collided and crashed around 1:20 p.m., the Federal Aviation Administration said in a statement. The collision occurred during the Commemorative Air Force Wings Over Dallas show.

The B-17, an immense four-engine bomber, was a cornerstone of U.S. air power during World War II. The Kingcobra, a US fighter plane, was used mostly by Soviet forces during the war. Most B-17s were scrapped at the end of World War II and only a handful remain today, largely featured at museums and air shows, according to Boeing.

Several videos posted on Twitter showed the fighter plane appearing to fly into the bomber, causing them to quickly crash to the ground and setting off a large ball of fire and smoke.

“It was really horrific to see,” Aubrey Anne Young, 37, of Leander. Texas, who saw the crash. Her children were inside the hangar with their father when it occurred. “I’m still trying to make sense of it.”

A woman next to Young can be heard crying and screaming hysterically on a video that Young uploaded to her Facebook page.

Air show safety – particularly with older military aircraft – has been a concern for years. In 2011, 11 people were killed in Reno, Nevada, when a P-51 Mustang crashed into spectators. In 2019, a bomber crashed in Hartford, Connecticut, killing seven people. The NTSB said then that it had investigated 21 accidents since 1982 involving World War II-era bombers, resulting in 23 deaths.

Wings Over Dallas bills itself as “America’s Premier World War II Airshow,” according to a website advertising the event. The show was scheduled for November 11-13, Veterans Day weekend, and guests were to see more than 40 World War II-era aircrafts. Its Saturday afternoon schedule included flying demonstrations including a “bomber parade” and “fighter escorts” featured the B-17 and P-63.

Videos of previous Wings Over Dallas events depict vintage warplanes flying low, sometimes in close formation, on simulated strafing or bombing runs. The videos also show the planes performing aerobatic stunts.

The FAA was also launching an investigation, officials said.