(CNN) -- An air-supported roof over the Dallas Cowboys' practice field collapsed during a heavy thunderstorm Saturday afternoon, leaving 12 people injured, authorities said.
About 70 people, including more than two dozen of the team's rookies, were in the facility when it was blown down shortly before 3:30 p.m. (4:30 p.m. ET), team officials said.
Two or three suffered serious injuries, but none were believed to be in life-threatening condition Saturday night, said Dr. Paul Pepe, Dallas County's emergency medical services chief.
CNN affiliate WFAA reported Cowboys special teams coach Joe DeCamillis, the son-in-law of former NFL head coach Dan Reeves, suffered a broken back. DeCamillis was seen on a stretcher wearing a neck brace.
A line of heavy thunderstorms was moving through the Dallas area at the time, he said, but no other damage to buildings was reported, said Mike Adams, a dispatcher for the Irving, Texas, fire department.
Arnold Payne, a photographer for WFAA, was shooting the Cowboys' practice session when rain began falling "tremendously hard."
"I noticed the walls started to waver ... and then I noticed that the lights that were hanging from the ceiling started to sway, and it wouldn't stop," Payne told CNN. Shortly after that, he said, "It was as if someone took a stick pin and hit a balloon."
Payne said Cowboys staff photographers were up in the metal framework beneath the canopy to film the practice session and "actually rode the building down with the storm." At least one was in surgery Saturday night, he said.
"There was nowhere for them to go, and it fell so fast -- it just collapsed as if it was being imploded," Payne said.
Video from CNN affiliate WFAA showed the roof caving in during a heavy storm, sending players, coaches and a handful of reporters and photographers scrambling to escape.
Cowboys' owner Jerry Jones told NBC that about 27 rookies from the NFL team and members of the team's coaching staff were inside the suburban Dallas facility at the time.
"They did not get good warning there, and the structure did collapse," Jones said, speaking from the Kentucky Derby in Louisville. "We're assessing who's injured at this particular time."