Fire spokeswoman Jennifer Spieser says initial reports do no indicate how serious the injuries are.
The casino is being developed by Rock Gaming in partnership with Caesar's Entertainment. A project spokeswoman says officials are assessing the situation.
Roads around the casino have been closed by police.
A partial collapse of a garage at another Ohio casino under construction occurred last month. That casino in Cleveland also is being developed by the Rock Gaming-Caesar's partnership. No one was injured in that collapse.
