Donald Trump sworn in as the 45th president of the United States
Mr Trump’s address at the event broke with tradition as he sought to hammer home populist political points against globalisation and the Washington elite.
Promising to “rebuild our country and restore its promise for all of our people”, he said: “From this day forward it is going to be only America first, America first.”
Around 1.8 million people turned out for president Barack Obama’s first inauguration in 2009, but only around 800,000 are thought to have travelled to Washington DC to see his successor sworn in at the Capitol building.
There were also ugly scenes on the streets nearby as anti-Trump protesters clashed with his supporters. Building windows were damaged by people carrying metal poles and hammers, and police used hand-held water cannon and pepper spray to disperse the troublemakers.
The trouble led to the arrest of around 100 protesters, with two police officers being injured, according to reports last night.
Similar protests took place around the world as Mr Trump took the presidential oath of office on the steps of the Capitol building just before noon local time, with his family and the outgoing president watching.
Delivering his inaugural address, Mr Trump said: “Every decision on trade, on taxes, on immigration, on foreign affairs will be made to benefit American workers and American families.
“We must protect our borders from the ravages of other countries making our products, stealing our companies and destroying our jobs.”
He added: “America will start winning again, winning like never before.”
His pronouncements were met with raised eyebrows by some in the UK, with prominent Labour backbencher Chris Bryant calling it “the most embarrassingly vacuous speech I have ever heard” and labelling it “cod nationalism”.
Other Labour MPs questioned how successful Britain’s goal of a free trade deal with the US could now be, but Foreign Secretary Boris Johnson took a more conciliatory tone, tweeting his congratulations and adding: “Look forward to continuing strong UK-US bond.”
First Minister Nicola Sturgeon also offered her congratulations, saying she wished the Trump administration well when dealing with “great global challenges”.
Imploring the US to come together, Mr Trump said that a united America was “totally unstoppable”.
Watched by Melania, his wife and the new First Lady, as well as Mr Obama and his wife, Michelle, and former presidents George W Bush, Bill Clinton and Jimmy Carter, the new president said: “We are one nation, and their pain is our pain, their dreams are our dreams and their success will be our success. We share one heart, one home and one glorious destiny. America will start winning again, winning like never before.
“We will bring back our jobs, we will bring back our borders, we will bring back our wealth and we will bring back our dreams.”
Mr Trump wasted no time in settling into his role. Policies have already appeared on the White House website, with Mr Trump saying he was “committed to eliminating harmful and unnecessary policies such as the Climate Action Plan and the Waters of the US rule”.
He has also announced plans to develop a missile defence system to protect the US against attacks from Iran and North Korea.