ABC News photographer Chris Plater at first thought he heard the sound of construction while near a Metro stop in downtown Washington, D.C., on Wednesday. He soon realized something more serious had happened.

“Immediately, I went forward to see what was going on,” he told ABC News Live. “I see two National Guard members down, and people are working on them, providing first aid.”

Plater filmed the frantic first response moments after the two National Guard members were shot near the White House in what officials called an apparent “targeted” attack. The incident was reported at 2:20 p.m. ET at the entrance to the Farragut West Metro station, according to a D.C. police official.

“It was just all here, you know, just a lot of people just running the opposite way, through the park and past me,” Plater said. “One person said something like, you know, man, the guy went up there and started shooting at the National Guard.”

Stacey Walters told ABC News Live that she was traveling in an Uber at the time of the shooting. 

“I heard ‘boom boom’ twice,” she said. “I was looking at my cellphone and my Uber driver said, ‘Why are all these people running?'”

She said she looked out the window and heard an adult telling young children to run. 

“Then I heard someone yell, ‘Help, help,’ in the direction of the shooting,” she said.

A law enforcement officer told them to turn the vehicle around, she said.

“It is such a beautiful day, you know, that’s the first thing I thought about, like, who would do this? It’s getting ready to be the holidays,” she said. 

She was struck by the sight of the children running from the scene. 

“They were on both sides of the road. Little, little children running,” she said.

The two National Guard members shot were a woman and man, according to a law enforcement official briefed on the situation. Both were in critical condition, FBI Director Kash Patel said Wednesday.

A lone suspect is in custody, authorities said. The unidentified male suspect was shot during the incident and transported to a hospital for treatment, police said.

Multiple law enforcement agencies, including U.S. Marshals, the Bureau of Alcohol, Tobacco, Firearms and Explosives, and the FBI, responded to the shooting. Department of Homeland Security Secretary Kristi Noem said her agency was working with local authorities to gather more information.

ABC News’ Briana Stewart, Jay O’Brien, Luke Barr, Pierre Thomas, Josh Margolin and Aaron Katersky contributed to this report.