Two World War II-era planes collided at an air show in Dallas on Saturday, US authorities said. Social media footage showed the planes colliding and hitting the ground in a fiery explosion.

It wasn’t immediately clear how many people were on the two planes, a Boeing B-17 Flying Fortress and a smaller Bell P-63 Kingcobra, the Federal Aviation Administration said.

It was also not clear if anyone survived the early afternoon crash, which occurred during the Wings Over Dallas airshow at Dallas Executive Airport.

While the number of casualties was not immediately known, “no bystanders or others injured on the ground were reported,” Dallas Mayor Eric Johnson tweeted.

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

After the collision, the planes appeared to break up into several large pieces before falling to the ground and exploding in a fireball, creating a huge plume of black smoke.

The crash scattered debris across the airport grounds, as well as onto a nearby freeway and mall, Johnson said.

The FAA said its agents and the National Transportation Safety Board were investigating the incident.

“As many of you have now seen, today during an air show we had a terrible tragedy in our city. Many details remain unknown or unconfirmed at this time,” Johnson said.

The B-17, a four-engined bomber, played an important role in defeating Germany in the air during World War II. With a reputation as a workhorse, it became one of the most-produced bombers of all time.

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

One of the last major B-17 crashes occurred on October 2, 2019, when seven people died in an accident at an airport in Windsor Locks, Connecticut.