Coursen watched the shooting from his cab window.
"I thought to myself, 'The car is getting blocked in. The car is going to surrender,'" he said. "Now the cop has his weapon out. The car kept trying to get away. Then he fired shots."
Senate Sergeant-at-Arms Terrance Gainer said a child was taken from the car to a hospital but said he knew of no harm to the youngster. Tourist Edmund Ofori-Attah said the child appeared to be about 2 to 3 years old.
A police officer was injured in the traffic accident but Gainer said the injuries were not life threatening.
"We heard three, four, five pops," said Sen. Bob Casey, D-Pa., who was walking from the Capitol to an office building across the street. Police ordered Casey and nearby tourists to crouch behind a car for protection, then hustled everyone into the Capitol.
"There were multiple shots fired and the air was filled with gunpowder," said Berin Szoka, whose office at a technology think tank overlooks the shooting scene.
The shooting comes two weeks after a mentally disturbed employee terrorized the Navy Yard with a shotgun, leaving 13 people dead including the gunman.
Before the disruption, lawmakers had been trying to find common ground to end a government shutdown. The House had just finished approving legislation aimed at partly lifting the government shutdown by paying National Guard and Reserve members.
U.S. Capitol Police on the plaza around the Capitol said they were working without pay as the result of the shutdown.
Associated Press writers Adam Goldman, Mark Sherman, Philip Elliott, Jesse Holland, David Espo, Alan Fram, Eric Tucker, Brett Zongker and Donna Cassata contributed to this report.