Four people have been killed in a shooting at a Tulsa medical building on a hospital campus.

The shooter was also dead, police Captain Richard Meulenberg said. It was unclear how the shooter died or what prompted the deadly assault.

“Officers are currently going through every room in the building checking for additional threats,” police said in a Facebook post on Wednesday night (local time).

“We know there are multiple injuries, and potentially multiple casualties.”

Captain Meulenberg said multiple people were wounded and the medical complex was a “catastrophic scene”.

St Francis Health System locked down its campus on Wednesday afternoon because of the situation at the Natalie Medical Building.

The Natalie building houses an outpatient surgery centre and a breast health centre.

Tulsa resident Nicholas O’Brien, whose mother was in a nearby building when the shooting occurred, said he rushed to the scene.

“They were rushing people out. I don’t know if some of them were injured or just have been injured during the shooting, but some of them couldn’t walk very well. But they were just kind of wobbling and stumbling and getting them out of there,” he said.

“I was pretty anxious. So once I got here and then I heard that she (his mother) was OK, the shooter had been shot and was down, I felt a lot better. It still is horrible what happened.”

A reunification centre for families to find their loved ones was set up at a nearby high school.

Agents from the Bureau of Alcohol, Tobacco, Firearms and Explosives were also at the scene, a spokesperson said.

The shooting came eight days after an 18-year-old gunman armed with an automatic rifle burst into Robb Elementary School in Uvalde, Texas, and killed 19 children and two teachers before being fatally shot himself.

It also came slightly more than a fortnight after shooting at a Buffalo supermarket by a white man who is accused of killing 10 black people in a racist attack.

On Wednesday prosecutors charged 18-year-old Payton Gendron with domestic terrorism. Gendron, who describes himself as a white supremacist, is accused of shooting 13 people in total during the massacre – almost all of them black.

He will also face 10 separate first-degree murder charges.

The domestic terrorism charge filed on Wednesday accuses the suspect of killing “because of the perceived race and/or colour” of his victims.

There were also multiple mass shootings nationwide over the recent US Memorial Day weekend, even as single-death incidents accounted for most gun fatalities.

-with AAP