President Donald Trump promises to rebuild America for 'all of our people'
'Whether we are black or brown or white we all bleed the same red blood'
Donald Trump pledged to put "America first" and vowed to "rebuild our country and restore its promise for all of our people" as he was sworn in as the 45th president of the United States.
The new president took the oath of office on the steps of the Capitol building as his family and outgoing president Barack Obama watched.
A Bible between them, Mr Trump was sworn in by Chief Justice John Roberts just before noon local time (5pm), before the two men shook hands.
President Trump's address broke with tradition as he sought to hammer home political points against globalisation.
Imploring the country to come together, he said that a united America "is totally unstoppable".
Delivering his inaugural address, President 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."
Promising to "make America great again", President Trump said: "From this day forward it is going to be only America first, America first."
The president went on: "But that is the past and now we are looking only to the future.
"We, assembled here today, are issuing a new decree to be heard in every city, in every foreign capital and in every hall of power.
"From this day forward, a new vision will govern our land. From this day forward, it's going to be only America first. America first."
The declaration won loud applause from the crowds on the National Mall.
Mr Trump continued: "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.
"Protection will lead to great prosperity and strength. I will fight for you with every breath in my body and I will never, ever let you down."
President Trump said: "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.
"We will build new roads and highways and bridges and airports and tunnels and railways all across our wonderful nation.
"We will get our people off welfare and back to work rebuilding our country with American hands and American labour.
"We will follow two simple rules, buy American and hire American."
President Trump said the US would "seek friendship and goodwill with the nations of the world" but with the understanding that it is the right of all countries to "put their own interests first".
"We do not seek to impose our way of life on anyone but rather to let it shine as an example.
"We will shine for everyone to follow."
Mr Trump promised to end Islamist extremism.
"We will reinforce old alliances and form new ones and unite the civilised world against radical Islamic terrorism, which we will eradicate completely from the face of the Earth," he said.
He followed the pledge with a call for open debate underpinned by unity.
"At the bedrock of our politics will be a total allegiance to the United States of America and through our loyalty to our country, we will rediscover our loyalty to each other," the president said.
"When you open your heart to patriotism, there is no room for prejudice.
"The Bible tells us how good and pleasant it is when God's people live together in unity.
"We must speak our minds openly, debate our disagreements honestly but always pursue solidarity.
"When America is united, America is totally unstoppable."
Mr Trump said "there should be no fear" and that all Americans "will always be protected" by "the great men and women of our military and law enforcement and most importantly, we will be protected by God".
The president promised to be different to politicians who are "all talk and no action".
"We must think big and dream even bigger," he said.
"In America we understand that a nation is only living as long as it is striving.
"We will no longer accept politicians who are all talk and no action, constantly complaining but never doing anything about it.
"The time for empty talk is over, now arrives the hour of action.
"Do not allow anyone to tell you that it cannot be done.
"No challenge can match the heart and fight and spirit of America.
"We will not fail, our country will thrive and prosper again."
Mr Trump said the US was "ready to unlock the mysteries of space, to free the Earth from the miseries of disease and to harness the energies, industries and technologies of tomorrow".
And he sought to address allegations of racism.
"A new national pride will stir ourselves, lift our sights and heal our divisions," the president said.
"It's time to remember that old wisdom our soldiers will never forget - that whether we are black or brown or white we all bleed the same red blood of patriots.
"We all enjoy the same glorious freedoms and we all salute the same great American flag.
"And whether a child is born in the urban sprawl of Detroit or the windswept plains of Nebraska, they look up at the same night sky, they fill their heart with the same dreams, and they are infused with the breath of life by the same almighty creator."
Mr Trump finished his address on the theme of his campaign promise to "make America great again".
He said: "So to all Americans in every city near and far, small and large, from mountain to mountain, from ocean to ocean, hear these words - you will never be ignored again.
"Your voice, your hopes and your dreams will define our American destiny, and your courage and goodness and love will forever guide us along the way.
"Together we will make America strong again.
"We will make America wealthy again.
"We will make America proud again.
"We will make America safe again.
"And yes, together, we will make America great again."
Earlier there were muted scenes as Mr Obama left the White House for the last time before accompanying then president-elect Trump in a motorcade to the Capitol building, joining their wives, vice-presidents and former presidents for the swearing in ceremony.
Among them were former president Bill Clinton and his wife Hillary, who was defeated in a bitter presidential campaign that divided America.
She appeared steely-eyed as she awaited Mr Trump's arrival ahead of the ceremony, but tweeted: "I'm here today to honor our democracy & its enduring values. I will never stop believing in our country & its future."
Mr Obama sent his own valedictory message to the American people, urging them to believe "not in my ability to bring about change, but in yours".
He tweeted: "It's been the honor of my life to serve you. You made me a better leader and a better man."
An estimated 800,000 people are thought to have travelled to Washington for President Trump's inauguration - not all of them supporters.
There were ugly scenes on the streets of the capital as protesters smashed windows, attacking buildings and clashing with both police and Trump supporters.
Similar protests took place around the world as President Trump was sworn in.
Party time in Moscow?
Champagne corks popped in Moscow as Russians celebrated the start of Donald Trump's presidency, confident of better relations ahead between the two countries.
"It's weird, but it's great, and for the first time ever Russians are applauding the victory of a US presidential candidate. It's a sign of the times," political analyst Stanislav Byshok said.
Mr Trump's promises to fix ravaged relations with Moscow have elated Russia's political elite following spiralling tensions with Washington over the Ukrainian crisis, the war in Syria and allegations of Russian meddling in the US election.
"We are ready to do our share of the work in order to improve the relationship," prime minister Dmitry Medvedev said on Facebook.
About 100 Trump sympathisers, nationalists and spin doctors gathered at a hipster party just a few hundred metres away from the Kremlin to celebrate on Friday, with a triptych of Mr Trump, Russian president Vladimir Putin and French nationalist politician Marine Le Pen in the centre of the hall.
An hour before Mr Trump took to the stage in Washington, the sound of opening champagne bottles echoed in the vaulted hall.
The party was co-sponsored by the conservative Tsargrad TV channel, which is led by ultra-right ideologue Alexander Dugin.
"Yes, it's a holiday," said a beaming Dmitry Rode, a communications executive with a glass of champagne in his hand.
"We all hope that relations between our countries and, more importantly, between our peoples will help to develop our economies. We're neighbours, we're just 50 kilometres (30 miles) away from each other."
Some party-goers wore Guy Fawkes masks, associated with hackers, in a sly reference to charges that Russia interfered in the US election.
"I'm happy for all Russian hackers," said 27-year old Filip Nikolsky, who wore a sweatshirt with the You've Been Hacked slogan.
He said he does not know if the allegations are true but "if it's true, why shouldn't we be happy?"
Still, the mood at the party in central Moscow was subdued compared with outbursts of joy at the news of Mr Trump's victory in November.
Revellers on Friday watched Mr Trump make his inauguration speech in silence, and no-one stood up for the American anthem, although the host suggested that all Americans should do so.
At another Moscow nightclub, several dozen people began toasting Mr Trump late on Thursday.
Willi Tokarev, 82, a singer who emigrated to the US in the mid-1970s and later became a music star in Russia, topped the entertainment bill with his song Trumplissimo America!
Mr Trump's praise for Mr Putin has raised expectations that he could move to normalise ties, although Mr Trump has not articulated a clear policy and some of his cabinet nominees have made hawkish statements on Russia.
Leonid Slutsky, the head of the foreign affairs committee in the lower house of parliament, expressed hope that Mr Trump will move to establish constructive ties with Moscow, but cautioned that there is no "magic button" to instantly achieve that.
"We expect a slow but steady revival of our relations," he said.
Dmitri Trenin, director of the Carnegie Moscow Centre, predicted that Russia will face a pragmatic but very tough partner in Mr Trump.
"Russia's potential is incomparable to that of the United States," he said, adding that Moscow will have to apply a lot of skills "to play from the position of weakness and not lose".
Speaking at the World Economic Forum in Davos, Switzerland, Russian deputy prime minister Igor Shuvalov voiced hope that Mr Trump will work with Mr Putin on solving the Ukrainian crisis and other problems, but warned against expectations of quick progress.
"Difficulties will remain," he said.