Dayton fire spokesman Bryan Adams said the fire was related to the construction work at the site, but couldn’t comment further since the investigation is still considered open.
The fire sent a large column of pitch-black smoke billowing, visible as far away as Troy and Beavercreek.
Traffic in parts of downtown came to a standstill as officials blocked off streets for safety and as crowds formed to watch the spectacle.
"Pieces of charred black material are floating off the building and landing on the street," said Steve Brack, a GrubHub driver that was making lunchtime deliveries downtown.
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The building will be first newly constructed office tower in downtown Dayton in about a decade.
According to Dayton fire officials, everyone was able to get out of the building safely, and the only people believed to have been inside at the time the fire started were construction workers.
The heavy black smoke rising over downtown may have looked dramatic, but the fire was not particularly large or hazardous, said Dayton fire Chief Jeffrey Payne.
“This wasn’t a dangerous fire because it was outside and well ventilated,” he said.