Washington DC will turn into a virtual fortress ahead of Donald Trump's presidential inauguration on Friday (Saturday NZ time).
Mr Trump has arrived in the US capital and begins a weekend of official events, starting with a lunch with his incoming cabinet and formal wreath-laying at the Arlington cemetery ahead of his swearing in.
Police have forecast that about 900,000 people, both supporters and opponents, will flood Washington for the inauguration ceremony.
The ceremony on Friday (Saturday morning NZT) includes the swearing in on the steps of the US Capitol and a parade to the White House along streets thronged with spectators.
Some of those attending will be protesting at New York real estate developer's demeaning comments about women, immigrants and Muslims, a vow to repeal the healthcare reform law known as Obamacare and plans to build a wall along the US-Mexico border.
His supporters admire Mr Trump's experience in business, including as a real estate developer and reality television star, and view him as an outsider and problem-solver.
Outgoing Department of Homeland Security secretary Jeh Johnson said police aimed to separate groups to defuse tensions.
"The concern is some of these groups are pro-Trump, some of them are con-Trump, and they may not play well together in the same space," Mr Johnson told MSNBC.
About 28,000 security personnel, kilometres of fencing, roadblocks, street barricades and dump trucks laden with sand will be part of the security cordon around almost 8 sq/km of central Washington.
About 30 groups that organizers claim will draw about 270,000 protesters or Trump backers have received permits for rallies or marches before, during and after the swearing-in. More protests are expected without permits.
A protest group known as Disrupt J20 has vowed to stage demonstrations at each of 12 security checkpoints and block access to the festivities on the grassy National Mall.
By far the biggest protest will be the Women's March on Washington on Saturday, which organizers expect to draw 250,000 people. Hundreds of women's march-related protests are scheduled across the US and around the world.
Police and security officials have pledged to guarantee protesters' constitutional rights to free speech and peaceable assembly.
Friday's crowds are expected to be less than the 2 million who attended Obama's first inauguration in 2009, and in line with the million who were at his second, four years ago.
Mr Trump will attend an interfaith prayer service at the cathedral at the end of the inaugural ceremonies.