Former Prime Minister Helen Clark has joined a chorus of people around the world in condemning the riots and severe unrest in the US Capitol Building.

"Never in one's wildest imagination could one have envisaged the dangerous events involving mob violence unfolding in Washington DC today," Clark said on Twitter this morning.

"An invasion of the premises of a democratic legislature anywhere is an affront to democracy and the rule of law and must be condemned as such."

Her comments are in response to the US Capitol Building – which houses the US' main centre of Government – being stormed by pro-Trump rioters.

They have made their way to the Senate floor and have clashed with the few police on the scene – the National Guard has been called in.

Never in one’s wildest imagination could one have envisaged the dangerous events involving mob violence unfolding in Washington DC today. An invasion of the premises of a democratic legislature anywhere is an affront to democracy and the rule of law and must be condemned as such. https://t.co/FMrQGjgexX

— Helen Clark (@HelenClarkNZ) January 6, 2021

Senators and Vice-President Mike Pence have been evacuated but there are still a number of officials and journalists within the building.

There are reports of some of the rioters breaking into the heavily fortified office of Speaker Nancy Pelosi.

She has demanded that outgoing President Donald Trump call on the rioters to leave the Capitol Building.

So far, however, Trump has refused to do so despite the fact the riots have been on-going for hours.

But in a tweet, he did say: "I am asking for everyone at the U.S. Capitol to remain peaceful. No violence! Remember, WE are the Party of Law & Order – respect the Law and our great men and women in Blue."

His tweets have come under fire for not explicitly asking the rioters to leave the building.

Trump has just 14 days left in the top job but for months he has been baselessly claiming the election was rigged.

He will be replaced by Joe Biden - who told reporters that what was happening was nothing short of an "assault on the rule of law" and an "assault on democracy".

He called on the "mob to pull back" and allow democracy to go forward and for Trump to "fulfil his oath" and demand an end to this siege.

The protesters are attempting to stop Congress from affirming President-elect Biden's victory in the November presidential election.

Congress was due to officially count the Electoral College votes - normally a formality - this morning (NZT).