Four people have been killed and eight have been injured - including two police officers - in a shooting at a bank in Louisville, Kentucky, police have said.

One of the officers is in a critical condition, Louisville Metro Police Deputy Chief Paul Humphrey added, and the shooter is among five pronounced dead.

Police named the gunman as Connor Sturgeon, a 23-year-old who worked at the bank as an employee.

Officers said Sturgeon, who had no prior contact with the police, joined the branch of the Old National Bank as a full-time employee last year.

They also named the victims as Tommy Elliott, 63, Juliana Farmer, 57, Jim Tutt, 64, and Josh Barrick, 40.

Officers who arrived on the scene on East Main Street "encountered active gunshots still being fired inside the location at that time," Mr Humphrey said.

"The shooter was confirmed to be dead on the scene."

Department Chief Jacquelyn Gwinn-Villaroel told a news conference that Sturgeon, who was using a rifle, shot at officers who then returned fire.

"The suspect shot at officers. We then returned fire and stopped that threat."

One officer was shot in the head and underwent surgery, the police chief said. The officer, who had recently graduated from the police academy, was in critical condition, she added.

Two other victims, one of whom is another police officer, were also in critical condition.

Louisville mayor Craig Greenberg condemned the attack, telling reporters at a press conference: "Let's be clear about what this was. This was an evil act of targeted violence."

He also thanked the emergency response in the city, adding "without a doubt, their actions saved lives".

"We will come together as a community to work to prevent these horrific acts of gun violence from continuing here and around the state," he said.

Kentucky Governor Andy Beshear said that he knew some of the victims, including Elliot, a senior vice president at the bank, which is not far from the minor league ballpark Louisville Slugger Field and Waterfront Park.

"This is awful," he said, on the verge of tears as he spoke.

"I have a very close friend who didn't make it today. And I have another close friend who didn't, either. And one who's at the hospital that I hope is going to make it through."

"These are irreplaceable, amazing individuals that a terrible act of violence tore from all of us," the governor said of the victims.