At least four people are dead and multiple people are injured following a shooting at the Natalie Building at Saint Francis Hospital in Tulsa, Oklahoma, on Wednesday evening, according to police.

Dispatchers received a 911 call shortly before 5 p.m. local time about a man walking with a rifle at the Natalie Building, a physicians' office building on the Saint Francis Hospital campus. When police responded, they said it turned into an active shooter situation, according to Tulsa Police Capt. Richard Meulenberg.

When police entered the building, they found multiple people shot in one area on the second floor, including in an orthopedic office, authorities said. The victims could be a combination both of employees and visitors, authorities initially said.

"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 told ABC News. "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."

The Tulsa shooting comes amid a spate of shootings in the U.S., including the Uvalde shooting in Texas where 21 people -- including 19 children -- were killed, and a mass shooting at a Buffalo, New York, supermarket that saw 10 Black people shot dead.