A bank employee shot dead four people in a “senseless” rampage at his Kentucky workplace before he was killed in a shootout with police.

Officers arrived within three minutes to find the male suspect still firing at the Old National Bank in downtown Louisville at about 8.30am Monday (local time).

In total five people are dead, including the shooter who was armed with a rifle and was initially identified as an ex-employee.

Two police are among nine people wounded.

One of the officers, Nickolas Wilt, 26, remains in a critical condition after being shot in the head and undergoing brain surgery.

The shooter, identified as Connor Sturgeon, 23, was live streaming the attack, according to Louisville Metropolitan Police Department interim chief Jacquelyn Gwinn-Villaroel.

“Unfortunately, that’s tragic. To know that that incident was out there and captured,” she said.

Police hoped to have the footage taken offline, she said.

Sturgeon had joined the branch of the Old National Bank as a full-time employee last year.

Among those fatally hit was a close friend of Kentucky’s Governor Andy Beshear, a Democrat, who fought back tears as he addressed media.

“This is awful. I have a very close friend who didn’t make it today,” he said, his voice breaking.

The victim Tommy Elliott, 63, had “helped me build my law career. Help me become governor. Gave me advice on being a good dad”.

“He was an incredible friend,” the governor said.

The other victims were named as Jim Tutt, 64, Josh Barrick, 40, and
Juliana Farmer, 57.

One man whose wife was inside the bank during the terrifying ordeal told how she hid in the vault to save her life.

His wife called him from the vault in a “very traumatic phone call to get” and asked him to alert 911.

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US President Joe Biden called the bank attack “a senseless act of gun violence” and said too many Americans were paying for “inaction” on gun control with their lives.

“When will Republicans in Congress act to protect our communities?”

Nine people wounded in the attack were treated at the University of Louisville hospital, a hospital spokesperson said, including the two police officers.

The mayor of the city of 625,000 people, Craig Greenberg said: “We will come together as a community to work to prevent these horrific acts of gun violence from continuing here and around the state.”

Mass shootings have become recurrent in the United States.

The shooting happened in a bank branch in downtown Louisville, Kentucky. Photo: AAP

So far this year, the country has experienced 146 mass shootings — using the definition of four or more shot or killed, not including the shooter — according to the Gun Violence Archive, a nonprofit group.

In one of the most recent high-profile incidents, three nine-year-old students and three staff members were killed by a former student at a school in Nashville, Tennessee, on March 27.