US President Donald Trump agreed to handover to president-elect Joe Biden in order, after the latter was certified by Congress on Thursday morning as the 46th president of the United States.

"Even though I totally disagree with the outcome of the election, and the facts bear me out, nevertheless, there will be an orderly transition on January 20th,” reads part of his statement.

He went on to say that; "I have always said we would continue our fight to ensure that only legal votes were counted,” adding that: "While this represents the end of the greatest first term in presidential history, it’s only the beginning of our fight to make America Great Again!”

On Thursday morning, US lawmakers certified Joe Biden's election victory, hours after Trump supporters stormed the Capitol in an attack that killed four people.

US Vice-President Mike Pence started the resumed session on Wednesday evening, in which lawmakers counted and confirmed electoral votes, saying it had been a "dark day in the history of the United States Capitol". 

The session certified Biden's 306 votes to Trump's 232.

The mob - some of whom wore body armour - used chemical irritants to attack police, according to Washington Metropolitan Police Chief Robert Contee.

They shouted and waved pro-Trump and US flags as they roamed the halls, demanding the results of the presidential election be overturned.

One woman was shot by police, while three others died as a result of "medical emergencies", officials said.

The mob, which had been encouraged by President Trump, stormed the building in a bid to overturn the election result, suspending a Congress session.

The president-elect blasted the "insurrection".

President Donald Trump later called on them to "go home" while continuing to make false claims of electoral fraud. Twitter and Facebook later froze his accounts.

The action was targeting the joint session of Congress being held to certify Biden's election victory on 3 November. 

The invasion sent members of Congress scrambling for cover under their seats as tear gas was fired.