Washington (AFP) – A volley of shots rang out outside the U.S. Capitol building on Thursday, sending lawmakers and tourists scattering for cover and triggering a massive security operation.

An AFP photographer saw at least one person receiving emergency medical assistance on the north side of the complex, but there was no immediate official word of casualties.

Senators told reporters at the iconic Washington landmark, the seat of Congress, that they had heard up to six shots. Police sealed off the building as emergency vehicles converged at the scene.

“The incident involving gunshots fired on the Senate side of the Congressional Complex appears to be an isolated event and there is no current threat to the Senate community,” Capitol police said in a statement.

According to unconfirmed media reports, the incident began just over a mile away outside the White House when a car rammed a barricade.

The suspect fled to the Capitol, where his or her car was halted and shots were fired, according to reports citing Secret Service officials.

A police car was left badly damaged by what appeared to be a collision on Constitution Avenue, immediately outside the Capitol.

A group of tourists were escorted into the Capitol. One of them told AFP that there had been a chase involving a black car that then sped toward the building.

The incident was the second major security breach in the U.S. capital in less than three weeks, after a September 16 incident in which a deranged gunman stormed the nearby Navy Yard and killed 12 people.

About half an hour after the Capitol incident began, the security lockdown at the Capitol was eased and the doors reopened. There were unconfirmed reports that the shooter was in custody.

“We heard what was about four shots,” Senator Bernie Sanders had said as tourists and lawmakers rushed into the building to take cover and police hurried to secure the area.

Outside the Dirksen office building, which houses senators’ offices, staff members not sent home by the U.S. government shutdown could be seen taking cover behind trees and vehicles.

Every minute or so, the Capitol Police made a loudspeaker announcement: “If you are in an office building, remain sheltered in place.”

Emergency vehicles converged on the scene, focused on the north side of the iconic landmark.

The White House was also placed in lockdown, with Secret Service agents in tactical gear deploying around the building. The security alert was later partially lifted.

Senators told AFP they had been walking with colleagues from a nearby senatorial annex when they heard shots and been forced to take cover.

“We saw people dropping to the ground. Not hit, taking cover,” said Senator Sherrod Brown of Ohio.

Juan Vargas, a congressman from San Diego, told AFP a police officer ordered him to leave the area and to remove the gold lapel badge that identifies him as a congressman.

“Then I got a call immediately from my staff, saying ‘be careful, there’s been a shooting’,” he added.

Photo Credit: AFP/Jewel Samad