The circus had just entered its second act when the downpour started. The performers stopped their show and gave an ominous command -- "Run!"
The open flaps on the side of the circus tent -- which weren't tied down -- "started going crazy," spectator Brandon Isham told CNN affiliate WGME.
"Next thing you know, the wind picked up ... and took the tent with it."
The tent collapse in Lancaster, New Hampshire, killed two spectators and injured dozens of people Monday evening, officials said.
About 100 people were inside the tent when it came down around 5:30 p.m., Fire Marshal William Degnan said.
Degnan didn't release the names of the deceased, only describing them as a "young man and a young girl."
At least 27 people were hospitalized, representatives from two hospitals told CNN. It's unclear how many may have been taken to other hospitals.
Isham said his 4-year-old son suffered a head wound when a pole struck him. But his son is now resting at home.
"Luckily enough, we all got down safe," he said.
The cause of the collapse is under investigation. But the storm brought one-inch hail, 60 mph winds and lightning, authorities said.
Degnan said authorities will be looking into the setup of the tent as part of the investigation.