Two people were fatally shot and several more were injured in a shooting that took place outside a high school graduation ceremony in Richmond, Va., on Tuesday evening, the authorities said.

A 19-year-old male suspect was in police custody, Rick Edwards, the acting chief of the Richmond Police Department said at a news conference on Tuesday evening. “We think the suspect knew at least one of the victims,” he said.

The shooting took place just before 5:15 p.m. outside the Altria Theater. He said officers inside the venue had heard gunshots and responded to the scene, where they had found “multiple victims suffering from gunshot wounds.”

The two people killed were an 18-year-old male and 36-year-old male, Chief Edwards said at the news conference. The authorities have not released the identities of the victims.

The authorities have seized four firearms, but one of them is “unrelated” to Tuesday’s shooting, Chief Edwards said.

Five others were shot and sustained non-life-threatening injuries, he said. Multiple other people, he said, had gone to local hospitals with injuries other than gunshots, including one person who was “hit by a car during the melee.”

Matthew Stanley, a spokesman for Richmond Public Schools, confirmed that the shooting took place in Monroe Park, adjacent to the Altria Theater, immediately after a graduation ceremony for students of Huguenot High School. Another ceremony scheduled for Tuesday evening was canceled.

Clips posted to social media appeared to show the aftermath of the shootings. In one, emergency medical workers appeared to be administering CPR to a victim. Students were still wearing their gowns and caps. Other regalia were strewn across the ground.

Jonathan Young, a member of the Richmond City School Board, said he and his colleagues had just finished celebrating some 300 graduating students when he heard about 20 consecutive gunshots that “prompted a mad rush sprint to get back inside the building.” Emergency medical workers and police officers were quickly at the scene, he said, adding that he had seen many people who appeared to have been injured in what he described as a “stampede.” Mr. Young said his shock quickly turned to “disgust and to anger.”

A statement posted on the website for the Richmond Public Schools on Tuesday evening addressed families and staff members, saying that “after the Huguenot High School graduation ceremony, a shooting took place outside in Monroe Park.” The message said all public schools in the city would close on Wednesday as a cautionary measure.

“I’m just tired of seeing people get shot,” Jason Kamras, the superintendent of Richmond Public Schools, said at the news conference. “Our kids get shot, and I beg of the entire community to stop.”

“Our kids can’t take it,” Mr. Kamras said. “Our teachers can’t take it. Our families can take it anymore. I beg of you to stop.”