Police announced early Sunday morning, that the active shooter situation began in the city's Oregon District, which is near downtown Ohio.
The tweets from Dayton police early Sunday did not include further details, but described the Oregon District shooting as "a large scene and investigation".
The shooting in Dayton, a riverfront city of about 140,000 people in southwestern OH, came just 13 hours after a mass shooting at a Walmart store in El Paso, Texas, where 20 people were killed and 26 others wounded.
Witnesses comfort one another at the scene of a mass shooting on Sunday in Dayton, Ohio.
The Dayton Daily News said the latest shooting occurred at or near a tavern called Ned Peppers Bar. The shooting location was outside of a nightclub known as "Ned Peppers".
The same wording was also posted on the Facebook page for nearby Hole in the Wall bar.
The FBI has opened a domestic terrorism investigation into the Texas massacre, a source familiar with the investigation process said Saturday.
Trump tweeted praise of law enforcement and said that "information is rapidly being accumulated in Dayton".
US Rep. Marcia Fudge, D-Ohio, tweeted, "It is beyond time for our leaders to do what is necessary to enact laws that keep guns out of the hands of people wishing to do harm".
In a second tweet, he wrote, "God bless the people of El Paso Texas".
Miami Valley Hospital said it received 16 patients from the shooting, but their conditions were not immediately available, said spokeswoman Terrea Little. The 20 mass killings in the U.S.in 2019 that preceded this weekend claimed 96 lives.
Kettering Health Network spokeswoman Elizabeth Long said numerous victims from a shooting had been brought to hospitals in the local system, but did not have details on how many.