Dee Stephenson said she was seated near the stage and heard the main actor shout "watch out!"
"Then you could feel the debris literally coming down on you and then I got hit on the back by a large piece," she told The Associated Press. "It was a complete dust curtain. You couldn't see."
Scott Daniels, an American tourist who lives in the Dallas area, said he'd managed to buy a last-minute ticket to the acclaimed production just before show time.
"I was lucky to get one seat that they had left over," he told The Associated Press. About 40 or 45 minutes into the show, he said, he started hearing noises — and screaming.
"I thought, maybe this is part of the play," he said. "All of a sudden, plaster starts raining down, huge hunks of plaster ... The lights went out and everything filled with dust — everybody was coughing and choking."