Washington authorities are investigating a report that gunshots were fired near the White House on Friday.
An AK-47 assault rifle was recovered and several streets were shut down.
At least one suspect was still at large, NBC Washington reported.
Secret Service spokesman Edwin Donovan said two cars were seen leaving the area.
Edwin Donovan also said witnesses heard shots and saw the cars racing on Constitution Avenue toward 17th Street.
One of the vehicles was abandoned at 23rd and Constitution.
Police lost sight of one vehicle but they caught up with a possibly stolen Honda sedan near the Roosevelt Bridge, NBC Washington said.
Edwin Donovan said witnesses saw the driver get out and run across the Roosevelt Bridge toward Arlington, Virginia.
Sgt. David Schlosser of the U.S. Park Police said the agency received a report of shots fired near 16th Street and Constitution Avenue, between the White House and the Washington Monument, at about 9.30pm.
David Schlosser added that the White House did not appear to have been the focus of the incident.
President Barack Obama was in San Diego, California, at the time of the incident on his way to the APEC summit in Honolulu.