President-elect Donald Trump’s inauguration on Monday will take place inside the US Capitol rather than outdoors because of severe cold, the first time in 40 years that US presidential inaugural ceremonies will be moved indoors.

"There is an Arctic blast sweeping the Country. I don’t want to see people hurt, or injured, in any way," Trump said on his Truth Social platform.

"Therefore, I have ordered the Inauguration Address, in addition to prayers and other speeches, to be delivered in the United States Capitol Rotunda.”

The last time an inauguration was moved indoors because of the bitter cold was in 1985 for former Republican President Ronald Reagan's second swearing-in when the afternoon wind chill fell into the range of minus 10 to minus 20 F (minus 23 to minus 29 C).

The weather forecast for Washington on Monday predicts temperatures at the time of Trump's swearing-in to be around 19 F (minus 7 degrees C), but will feel even colder with wind chill.

Trump said supporters can view the ceremony on screens inside the Capital One Arena, a sports venue in downtown Washington that holds 20,000 people.

Work continues near the presidential reviewing stand on Pennsylvania Avenue outside the White House ahead of President-elect Donald Trump's inauguration. – AP

Trump also said his presidential parade, which was set to involve marching bands and other groups proceeding down Pennsylvania Avenue past the White House, will be switched to inside the Capital One Arena. It was not immediately clear how a parade would be organised inside the sports venue.

Trump said he would join the crowd at the arena after he is sworn in.

Trump is due to hold a rally with supporters inside the same arena on Sunday, the eve of his inauguration.

Bitter cold has had an impact on several past inaugurations.

William Henry Harrison, the ninth US president, delivered the longest inaugural address on March 4, 1841, in wet and cold conditions without a hat or overcoat.

That event and speech were thought to have contributed to his later succumbing to pneumonia. He died one month after taking office, making his presidency the shortest in American history.

During the second swearing-in ceremony for President Ulysses S. Grant on March 4, 1873, several cadets and midshipmen standing outside without overcoats collapsed and gusting winds made Grant's address inaudible to even those close to him on the platform, according to a history published by the National Weather Service. The morning low temperature of 4 F (-15 C) on that day remains Washington's coldest March day on record.

Key points about Trump's inauguration

Bad weather forecasts mean President-elect Donald Trump will take the oath of office from inside the Capitol Rotunda and people visiting Washington from around the country won't be able to see it in person.

The decision to move Monday's event indoors marks the first time in 40 years that such a change has been made. Plans are underway to accommodate some visitors in town for Trump's second inauguration at the city's pro basketball and hockey arena.

Where will Trump now be sworn in?

The Rotunda is prepared as an alternative for each inauguration in the event of inclement weather. The swearing-in was last moved indoors in 1985, when President Ronald Reagan began his second term. Monday's forecast calls for the lowest Inauguration Day temperatures since that day.

President Joe Biden, members of Congress and other dignitaries and notable guests will be able to view the ceremony from inside the Capitol.

How many members of the public can attend the inauguration inside?

In his social media post about the weather-related change, Trump said that "various Dignitaries and Guests" would be taken into the Rotunda for the ceremony, although it's unclear how many people that meant, or whom.

According to Trump's post, Capital One Arena — where the incoming president is holding a Sunday afternoon rally, an event he said Friday is still on — will be open again on Monday for "LIVE viewing of this Historic event." No information is available yet on how to sign up for a seat inside the arena Monday.

What about the parade — is it still happening?

Trump also said that Capital One Arena would "host the Presidential Parade," another tweak from tradition. Trump also said that he would "join the crowd" at Capital One after he takes the oath.

Normally, thousands of people line the route from the US Capitol to the White House, which the president typically traverses following the swearing-in ceremony. Marching bands and other participants from around the country come to Washington to participate, so presumably they will also be part of the newly arranged indoor festivities.

Are other inaugural events still happening?

According to Trump, yes. The Republican president-elect said on Friday that other inaugural events, including the Sunday rally and his participation in three inaugural balls on Monday night, would take place as scheduled.

How cold is it going to get on Monday?

The National Weather Service is predicting that the temperature will be around 22 degrees Fahrenheit (minus-6 Celsius) at noon Eastern time, when Trump becomes president. That would be the coldest since Reagan's second inauguration saw temperatures plunge to 7 degrees (minus-14 Celsius).

"The weather forecast for Washington, D.C., with the windchill factor, could take temperatures into severe record lows," Trump posted on his Truth Social platform. "There is an Arctic blast sweeping the Country. I don't want to see people hurt, or injured, in any way."

In 2009, it was 28 degrees (minus-2 Celsius) for President Barack Obama's swearing-in. Biden was sworn in four years ago in a relatively balmy 42 degrees (5.5 Celsius).

A few Democrats poked fun at Trump's decision. Minnesota Governor Tim Walz, who was Vice President Kamala Harris' running mate in the Democrats' losing 2024 campaign, posted a photo of himself standing in a snowstorm with the caption, "There's no such thing as bad weather, just bad clothing."