A man thought to be armed with four guns has killed two people and wounded five at a college graduation ceremony in Richmond, Virginia, United States, police said.

Police said they arrested one person, a 19-year-old man, yesterday near the theater where a graduation ceremony was held near Virginia Commonwealth University.

The suspect could be charged with two counts of murder and other counts, Richmond Police Chief Rick Edwards said at a news conference.

"When they heard gunshots, it was obviously chaos," he said. "We had hundreds of people at Monroe Reservoir, so people were scattered. There was a lot of chaos at the scene."