WASHINGTON (AP) — All through downtown Washington, the primary sound for several blocks was the beeping of forklifts unloading more fencing.

There were no cars or scooters and seemingly no tourists Wednesday, just the occasional jogger and multiple construction crews at work. The U.S. Capitol that proved such a soft target last week was visible only through lines of tall, black fence.

Two blocks from the White House, a group of uniformed National Guard troops emerged from a tour bus and headed into a hotel as a state of lockdown descended on Washington that will last through the Jan. 20 inauguration.

"Clearly we are in uncharted waters," said Washington Mayor Muriel Bowser.

Last week's "violent insurrection" at the Capitol by supporters of outgoing President Donald Trump has "impacted the way we are approaching working with our federal partners in planning for the 59th inauguration," Bowser said Wednesday.

The FBI has warned that armed protests by violent Trump supporters were being planned in all 50 state capitals as well as in Washington for the days leading up to the inauguration of President-elect Joe Biden.

Between the pandemic and the security threat, Bowser is flat-out asking people not to come to the District of Columbia for the inauguration. And at Bowser's request, a National Special Security Event declaration was moved up to Jan. 13, a distinction which she said "puts in place an entirely different command and control structure" for security.

The NSSE status is normal for a presidential inauguration and other major events like an international summit or the Super Bowl. But it's rare to start the lockdown so far in advance of the event.

Police vehicles sealed off a huge swath of downtown D.C. Wednesday, causing immediate traffic snarls. Starting Wednesday, Bowser said, anyone inside the inauguration perimeter might be stopped and questioned. Starting Friday, all parking garages in the downtown restricted zone will be sealed through the inauguration.

Bowser is also being pushed to deny lodging options to potentially violent protesters. The local Black Lives Matter affiliate and Shutdown DC issued a joint statement Wednesday urging all downtown hotels to voluntarily close and pay their staffs. In addition to the threat of violence, the activist groups say Trump supporters are a threat to the health of hotel staff for their general refusal to wear facemasks amid the pandemic. Several downtown hotels, including one which had become a favorite hangout of the militant Proud Boy faction, chose to avoid trouble by closing last week.

"Closing hotels completely for these six nights is the only way to guarantee the safety of hotel workers, neighbors, vulnerable and unhoused residents, incoming administration officials, members of Congress, and our democracy," the statement said. "If hotels do not willingly close, we ask Mayor Bowser to extend today's emergency order and close all hotels in the city."

On Wednesday, Airbnb announced it was cancelling all reservations in the Washington metro area. Bowser said she had been in regular contact with Airbnb officials since last week, but did not specifically request this step.

"We are aware of reports emerging yesterday afternoon regarding armed militias and known hate groups that are attempting to travel and disrupt the Inauguration," a company statement said. "We are continuing our work to ensure hate group members are not part of the Airbnb community."

On the ground, much of the most visible security will come in the form of more than 15,000 National Guardsmen from multiple states, some of them armed.

According to officials, the number of Guardsmen who will actually be carrying guns will be limited. Some Guard members nearer the Capitol will have long guns, and others will have their sidearms.

It is likely that those closer to the crowds or on fence lines won't be armed, but those up closer to the building may be. National Guard members operate under strict rules of engagement on the use of force. But generally speaking, troops can use lethal force to protect the lives of others and themselves.

Officials also said that while 15,000 Guard members have been activated, more may be called. D.C. Police Chief Robert Contee estimated Wednesday that more than 20,000 National Guardsmen would be active in the District of Columbia on Inauguration Day.

Officials are continuing to review requests from law enforcement, and some believe several thousand more could be brought in. Defense and military officials have been calling governors and adjutants general to ask if they might have people they could send, if requested.

So far, officials said state leaders have said that protecting their own capitols will be their top priority, but they still have some Guard members they will be able to send, if needed.