JOE Biden has been sworn in as the 46th president of the United States.

At age 78, he is the oldest president inaugurated.

By his side, Kamala Harris has become the first woman to hold the office of vice president of the US.

The former senator from California is also the first black person and first person of South Asian descent elected to the vice presidency, and will become the highest-ranking woman ever to serve in government.

First Minister Nicola Sturgeon, tweeted: “Warm congratulations and best wishes to President Biden and Vice President Harris. Scotland and the USA share long-standing bonds of friendship and co-operation.

“We look forward to building on these in the years ahead.”

Boris Johnson said he looks forward to working with the Democratic successor to Donald Trump.

The Prime Minister tweeted: “Congratulations to @JoeBiden on being sworn in as President of the United States and to @KamalaHarris on her historic inauguration.

“America’s leadership is vital on the issues that matter to us all, from climate change to Covid, and I look forward to working with President Biden.”

Former US president Barack Obama tweeted to his former vice president: “Congratulations to my friend, President @JoeBiden!

“This is your time.”