Security forces deployed tear gas as they chased men through the streets of Washington just one hour before official proceedings began.
Chaos erupted downtown in the city as miles from the suits and ties in the Capitol, hooded men and women are marching, throwing over bins, smashing windows and spray-painting buildings.
Police chased them with batons forcing the crowd to disperse across the streets.
Those caught were were doused with pepper spray.
More violence is expected as counter protest groups have arrived outside the White House to condemn or celebrate the billionaire businessman becoming president of the United States.
Those on the streets have said they are in the middle of a "riot".
Shop windows smashed by rioters in Washington
Images of smashed shop fronts and car windows have appeared on social media.
Trump has been inaugurated as the 45th President of the United States in a grand ceremony in Washington DC.
Trump's 35-word swearing-in took place on a 10,000 square foot specially-built platform in front of the Capitol that holds 1,600 people.
PROTESTS at Trump's Inauguration Day
Fri, January 20, 2017
Protestors were chased through the streets of Washington as violent scenes broke out close to the Donald Trump inauguration in Washington.
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Donald Trump will be inaugurated as the 45th president of the US with wife Melania by his side
— Cassandra Fairbanks (@CassandraRules) January 20, 2017
On Thursday evening, protesters clashed with police outside a pro-Donald Trump black tie event, called the 'DeploraBall'.
Footage posted on social media appeared to show police in riot gear using pepper spray and tear gas to disperse the protesters.
He will be being watched by thousands of security officials, police, FBI agents and will be being covered by snipers.
Uniformed officers have lined the streets in a bid to keep the crowds calm, while support in full riot gear wait behind them.
Earlier reports suggested there will be snipers waiting on roofs above Washington and scene kilometres around the White House blocked to cars.
Market analyst says markets are jittery over Trump uncertainty
Obama and Trump leave the Whitehouse together
Hilary and Bill Clinton attend Trump's inauguration
Police on the streets are swarming around protestors after some turned violent
Crowds gathered in Washington are being watched over by thousands of police and security
Dump trucks carrying sand have also been brought in to block streets.
At one checkpoint, Black Lives Matter protesters were chanting “Shut it down” before five men chained themselves together, preventing anyone from passing.
Trump supporters who have "lost friends" since visiting the ballot box said they were happy to be able to mix with others who believe in the new president.