Before Biden was sworn in, Kamala Harris took oath as the country first woman Vice President.

Biden, who is known around the world for his stint as the vice president during the Obama administration, is the oldest person ever to be sworn in as president of the country. He turned 78 in November 2020.

Ahead of the inauguration, the Democrat leader tweeted that it is a "new day in America".

"It's a new day in America," Biden wrote on Twitter only minutes after outgoing President Donald Trump flew out of Washington at the end of a controversial four-year presidency.

Trump left Washington on Wednesday just three hours ahead of the inauguration of his successor Joe Biden, saying it had been an "incredible four years" and promising to be "back in some form."

"I just want to say goodbye but hopefully it's not a long-term goodbye," Trump told reporters at the White House before he and First Lady Melania Trump walked a short red carpet and boarded Marine One for the helicopter ride to Joint Base Andrews.