US police have arrested a gunman after he shot and wounded a police officer inside the US Capitol building's visitor centre, officials said.
The massive complex was placed on lockdown, but the security precaution has since been lifted.
The Capitol Visitor Center is still closed, but the House and Senate have reopened for official business only.
Washington's city police called it an "isolated" incident, saying there is "no active threat" to the public.
Officials described the police officer's injuries as minor. The gunman was taken to a hospital, apparently also injured.
US Congress is on recess for the Easter holiday, but some members of Congress and staff members were on site.
To enter the US Capitol or any Senate or House office buildings, visitors must go through a metal detector and weapons are not permitted.
Diane Bilo, a woman from Ohio, told the Washington Post her husband heard the shot.
"My husband said he heard a shot followed by a full clip," she said.
Multiple members of Congress have posted to social media, reporting that their staff are safe and sheltering in place.
In 1998, an attacker shot and killed two police officers at the Capitol. The visitor centre was built as a way to strengthen security after the shooting.
Many tourists are in Washington for the annual Cherry Blossom festival - about 1.5 million people visit the city during the four weeks of the festival.
The White House was also put on lockdown temporarily due to a separate incident.