Protesters backing President Donald Trump have breached the US Capitol, forcing a delay in the constitutional process to affirm Joe Biden's victory in the November election.

Mr Trump urged his supporters to travel to Washington to protest over Congress' formal approval of Mr Biden's win.

Several Republican politicians have backed his calls despite there being no evidence of fraud or wrongdoing in the election.

Protesters are now inside the Senate chamber. One got up on the dais and yelled "Trump won that election".

Several dozen are roaming through the halls, yelling, "Where are they?" Some were also in the visitors' galleries.

Pressure is mounting on Donald Trump to condemn supporters who are violently clashing with law enforcement on Capitol Hill.

Among those urging President Trump to act is his former communications director, Alyssa Farah, who tweeted that he should "Condemn this now."

She said: "You are the only one they will listen to. For our country!"

President Trump has so far offered a single tweet, asking his supporters to "Please support our Capitol Police and Law Enforcement. They are truly on the side of our Country. Stay peaceful!"

His former chief of staff Mick Mulvaney tweeted: "The President's tweet is not enough. He can stop this now and needs to do exactly that. Tell these folks to go home."

His lawyer, Rudy Giuliani, also addressed Trump supporters in a tweet, calling them the "patriots challenging the fraudulent election".