Four people are dead and at least nine others are injured following a mass shooting at a bank in Louisville, Kentucky, on Monday morning, according to police.

The lone gunman opened fire in the Old National Bank's first-floor conference room at about 8:30 a.m. local time, according to officials.

The suspect had a connection to the bank, possibly a former employee, police said.

Eyewitnesses said the shooter appeared to have been armed with a long gun.

"He just started shooting," Troy Haste told ABC Louisville affiliate WHAS. "Whoever was next to me got shot. Blood is on me from it."

Officers arrived at the Old National Bank within three minutes of being dispatched and found the suspect still firing, Louisville police said.

Officers exchanged gunfire with the suspect who died at the scene, police said. It's not yet clear if the suspect's wounds were self-inflicted, police said.

Two officers and seven civilians were injured in the Louisville shooting, according to the University of Louisville Hospital.

One of those officers is in critical condition, according to police.

At least three patients have already been discharged, according to the hospital.