(CNN) -

Thirteen people, including children, were injured Wednesday when an experiment went awry at the Terry Lee Wells Nevada Discovery Museum in Reno, police said.

"Of the 13 injured, four were treated and released and nine were transported to a local hospital," Reno Officer Tim Broadway said.

"There were seven children and two adults taken to the hospital with chemical burns to their arms, hands and face. None of the injuries are life-threatening, but we do not know their exact condition," he said.

Broadway said they were hurt in an explosion caused by a tornado experiment, in which chemicals were mixed incorrectly. The Reno fire chief has called what happened a chemical flash, the officer said.

"We were watching fire tornadoes and it exploded," Jackie Rider told CNN affiliate KOLO. "It was terrifying. The one tornado wasn't going, no one really thought anything of it and then she was like, I forgot to add this and added it, then everything exploded."

She said her two daughters ages 6 and 4, a nephew and a niece were treated for burns on their arms and legs.

The museum tweeted that preliminary reports of an explosion were inaccurate.

"A routine science demonstration didn't happen as usual causing a flash," it posted. "The Discovery is focused on the safety of its visitors at this time. More information coming soon."

The museum describes itself as a hands-on facility that focuses on science, technology, art, engineering and math.