Kamala Harris will forgo an in-person speech to farewell her Senate seat amid concerns about the potential for violence by domestic extremists in the lead up the official end of Donald Trump’s presidency.

Two aides to incoming president Joe Biden are hopeful that the US presidential inauguration ceremony on Thursday (Australian time) will be a safe, outdoor event.

But ongoing security threats have more than a dozen US states on high alert after the Capitol building was attacked this month by supporters of outgoing President Donald Trump.

More than a dozen states have activated National Guard troops to help secure their capitol buildings.

US Vice President-elect Ms Harris will resign from her Senate seat on Tuesday (Australian time), two days before she and Mr Biden are inaugurated.

Fellow Democrat Alex Padilla will be appointed to serve the final two years of Ms Harris’ term.

Ms Harris will give no farewell Senate floor speech. The Senate is not scheduled to reconvene until Wednesday, the day before Inauguration Day.

“Our plan and our expectation is that President-elect Biden will put his hand on the Bible, with his family, outside, on the west side of the Capitol,” Kate Bedington, a top spokesperson, told US broadcaster ABC.

But the inauguration will take place on the steps outside of the US Capitol building, Ms Bedington said.

Holding the inauguration outdoors on the steps of the very building that was attacked has symbolic value, she said.

Trump supporters gathered at state capitol buildings throughout the nation on Sunday. Photo: Getty

“I think that will send an incredibly important visual image to the world about the resilience of American democracy,” she said.

Washington is facing tight security measures, with areas around the city centre, including the National Mall, shut down and thousands of National Guard troops deployed to the capital city.

Fences have been erected, cement blocks laid down and heavy trucks used to block traffic along main streets of the capital and arteries around the city.

The Federal Bureau of Investigations warned there was “online chatter” of potential attacks by Trump loyalists.

“We are concerned certainly about these threats,” the incoming White House Chief of Staff Ronald Klain told broadcaster CNN.

However, Mr Klain said he was convinced the Secret Service and troops “will keep the inauguration itself safe.”

There are additional concerns about violence in state capitals around the country, with some governors calling in additional forces to beef up security.

National Guard soldiers move through the Capitol Visitors Center for their guard shifts around the grounds of the US Capitol on Saturday. Photo: Getty

Security officials have eyed Sunday as the first major flashpoint, as that is when the anti-government “boogaloo” movement made plans weeks ago to hold rallies in all 50 states.

Capitals in battleground states, where Mr Trump has directed his accusations of voter fraud, were on especially high alert.

But by midday, only a few demonstrators had taken to the streets alongside hundreds of law enforcement officers and media personnel.

Four protesters with long rifles stood outside Michigan’s capitol in Lansing on Sunday, one wearing a tactical vest and a blue Hawaiian shirt and another wearing a Trump shirt and fatigue pants as he held a “Don’t tread on me” flag.

Nearby, crews had blocked off streets and office buildings in Lansing had boarded up their windows in anticipation of potential violence.

In Atlanta, several hundred law enforcement officers and National Guard troops milled around Georgia’s state house early on Sunday.

Chain-link fences and cement barriers protected the Capitol grounds and multiple armoured vehicles were stationed nearby.

In addition to increasing police presence, some states, including Pennsylvania, Texas and Kentucky, have taken the further step of closing their capitol grounds to the public.

-with AAP