WASHINGTON (AP) — A gunman was taken into custody after shots were fired in the U.S. Capitol complex on Monday, Capitol officials said, and visitors and staff were shut in their offices and told to "shelter in place."

Initial reports said a police officer sustained minor injuries, but later reports raised doubts about who, if anyone, was shot.

The event unfolded with Congress on recess and lawmakers back in their districts, but the Capitol complex teeming with spring tourists. The White House was briefly put on lockdown, although that was soon lifted. A notification sent to Senate offices said no further suspects appeared to be at large.

Capitol office buildings and the Capitol itself were re-opened for business about an hour after the initial reports of gunfire. The Visitors Center where the shooting occurred remained closed as the incident was being investigated.

Visitors were being turned away from the Capitol as emergency vehicles flooded the street and the plaza on the building's eastern side. Police, some carrying long guns, cordoned off the streets immediately around the building, which were thick with tourists visiting for spring holidays and the Cherry Blossom Festival.

Cathryn Leff of Temecula, California, in town to lobby with the California Association of Marriage and Family Therapists, said she was going through security at the main entrance to the Capitol Visitors Center when police told people to leave immediately.

Outside, on the plaza just to the east of the Capitol, other officers told those there to "get down behind this wall," she said. "I heard what sounded like two shots off to my left." After a while, police told her and others to keep running. "I felt like I was in a movie. It didn't feel real at all."

Traffic was jammed in the vicinity, but despite the obvious emergency the scene was relatively calm. A work crew on the north side of the Supreme Court, across the street, was asked to stop work and move away from the building as a precaution.

Capitol Police provided no immediate information but scheduled a press conference for later in the afternoon.

From back home in their districts, many lawmakers got in touch with staff to ensure all were safe, and posted thanks on Twitter as it appeared they were.

Earlier in the day, officials conducted an unrelated shelter-in-place drill at the Capitol.

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Associated Press writers Mark Sherman, Mary Clare Jalonick and Alan Fram contributed to this report.