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 victims were identified as Concord, Vermont, residents Robert Young, 41, and his 8-year-old daughter Annabelle, State Fire Marshal William Degnan said Tuesday. They died from blunt force trauma, according to an autopsy.
About 100 people were inside the tent when it came down about 5:45 p.m., Degnan said.
The circus did not have a required "place of assembly permit" from local fire officials, Degnan said. No local or state officials were involved in putting up the tent, he said.
"That is something that we're looking into," Degnan said of the permit. "They just went and set up and did it."
At least 39 people were hospitalized, representatives from four hospitals told CNN. At least 34 of those victims were discharged, the hospital officials said.
Degnan said at least 32 people were treated at four hospitals -- some transported by ambulance, others arriving on their own -- but that "information is still trickling in."
Spectators helped evacuate the wounded, he said.
"Most everybody played a role in helping get some of the people trapped in the tent out," he said.
Isham said his 4-year-old son is resting at home after suffering a head wound from a falling pole. "Luckily enough, we all got down safe," he said.
Wind, hail and lightning
The cause of the collapse is under investigation. But the storm brought 1-inch hail, 60-mph winds and lightning, authorities said.
About 23 minutes before the collapse, Degnan said, the National Weather Service -- which is assisting in the investigation -- had issued a severe thunderstorm warning for the region.
"It's really the responsibility of the show to monitor the conditions," he said. "We don't know why they were going on at that time and what they knew."
A aerial review traced the path of the heavy winds from about a half mile to a mile from the scene in what weather service officials described as a microburst, Degnan said.
"The path was very clear, when you look at it from the air, and how it took down some trees on a river bank and then spread out across a field and ultimately took down the tent," he said.
Degnan said authorities will be looking into the manufacturer's specifications as well as the setup of the tent as part of the investigation.
"At this time," Degnan said, "there's no indication that there will be any kind of charges."
He added, "Their responsibility is for the safety of their guests, whether they knew or not that the storm was coming. We'll be looking into that."
The circus, which has visited New Hampshire in previous years, has canceled the two shows scheduled for Tuesday in Bradford, Vermont, according to its website. As of now, the circus planned for Wednesday in Grafton, New Hampshire, is still happening, according to the Walker International Events tour calendar.
Circus officials have not been available for comment but Degnan said the "cooperation level has improved greatly and we're getting good information from them."