At least five people are dead, including the shooter, and several others were injured after a mass shooting took place at the Natalie Building at St. Francis Hospital in Tulsa, Oklahoma, on Wednesday, ABC News reports.

According to Tulsa Police Captain Richard Meulenberg, the department received a call of a man walking with a rifle near a medical facility. When police responded, it immediately became “an active shooter situation.”

As the officer entered the facility, they discovered that multiple people had been shot.

"Officers immediately rushed to the second floor where the shooting was taking place, when they got there they found a few people had been shot, a couple were dead at that time," Meulenberg said. "We also found at that time who we believe and still believe to be the shooter because he had a long rifle and a pistol with him."

Meulenberg noted that the shooter had shot himself dead after killing the others.

Officials stated that the gunman was upset about a recent back surgery that he had undergone was ineffective. He killed the doctor who had performed the surgery as well as three others. The gunman bought his weapons , including an AR-15 style rifle, just hours before he began his deadly rampage.

Police said the gunman had a letter on him stating that he blamed his surgeon for his continuing back pain and intended to kill him and anyone who got in his way as retribution.

As of June 1, this is the 233 mass shooting to take place in the U.S. The Tulsa shooting is the latest mass shooting in the wake of the recent Buffalo supermarket attack and the Uvalde, Texas elementary school killings.