Updated at 7:44 a.m. ET

In the second major mass shooting in less than 24 hours in the United States, officials say a gunman killed nine people and injured 26 early Sunday in Dayton, Ohio.

The shooter was killed by police officers.

“As a mayor this is a day that we all dread happening,” Dayton Mayor Nan Whaley told reporters Sunday morning.

Twenty-six people are in multiple hospitals across the city, some with life-threatening injuries, she said.

Police were already on patrol in the area full of nightclubs known as the Oregon District and stopped the shooter in less than one minute, the mayor said.

“It is a terrible day for Dayton but I am so grateful for Dayton police’s fast action,” she said, saying hundreds of people could have been killed based on the size of crowds in the area on a Saturday night.

“Dayton is a very safe area, downtown Dayton is a very safe area,” Lt. Col. Matt Carper of the Dayton Police Department had said earlier. “This is extremely unusual obviously for any community, let alone Dayton. And in our Oregon District, this is unheard of and very sad. It’s a very tragic evening,” he told reporters shortly after 4 a.m. Sunday.

Police say the shooting started at 1 a.m. outside. In what Carper called a “very short timeline of violence,” the shooter used what police called a “long gun.” Whaley later said the shooter wore body armor and used a .223 caliber weapon with a high-capacity magazine and had additional magazines.

Carper said police were investigating the possibility of more shooters being involved, but “it looks like” only one shooter was responsible.

Police did not identify the shooter and said they are working on identifying the suspect.

No police officers were injured.

The Dayton police have trained for years for active shooting situations, Carper said. Twenty-one medic units responded to the scene and the FBI is on the scene to assist in the investigation.

This is a developing story. Some things that get reported by the media will later turn out to be wrong. We will focus on reports from police officials and other authorities, credible news outlets and reporters who are at the scene. We will update as the situation develops.