Six people were killed after two historic military planes collided and crashed to the ground Saturday afternoon during a Dallas air show, officials said.

“According to our Dallas County Medical Examiner, there are a total of 6 fatalities from yesterday’s Wings over Dallas air show incident,” Dallas County Judge Clay Jenkins tweeted Sunday. He said authorities are continuing to work to identify the victims.

The Allied Pilots Association, the American Airlines pilots’ union, said on Twitter that two of its former members, Terry Barker and Len Root, were on board the B-17 and had died. 

The crash occurred around 1:20 p.m. Saturday, when the Boeing B-17 Flying Fortress and a Bell P-63 Kingcobra collided at the Wings Over Dallas Airshow at Dallas Executive Airport, according to information provided by the Federal Aviation Administration.

There were no reports of injuries on the ground, but Dallas Mayor Eric Johnson said the collision's debris field includes parts of Executive Airport grounds, Highway 67, and a nearby strip mall.

The B-17 would normally have a crew of four or five, and the Kingcobra would just have a pilot, Hank Coates, CEO and president of Commemorative Air Force, the organization behind the show, said at a news conference Saturday evening.

No paying customers were on board the B-17, he said. Because family needs to be notified of any possible fatalities, and because federal investigators have taken jurisdiction, Coates said he's unable to make manifests or information about fatalities public.

Both planes were part of the nonprofit organization's fleet of 180 aircraft used in its own air shows and those of other groups to demonstrate how the planes were used in World War II.

"This was a World War II flight-demonstration type of air show," Coates said. "It's very patriotic."

There was about an hour left in the show when the collision occurred, he said.