Washington: Washington will turn into a virtual fortress ahead of Donald Trump's presidential inauguration on Friday, as the U.S. capital braces for more than a quarter-million protesters expected during the Republican's swearing-in.

Police have forecast that some 900,000 people, both supporters and opponents, will floodWashington for the inauguration ceremony, which includes the swearing-in on the steps of the U.S. Capitol and a parade to the White House along streets thronged with onlookers.

Many of those attending will be protesters irate about the New York real estate developer's demeaning comments about women, immigrants and Muslims, a vow to repeal the sweeping healthcare reform law known as "Obamacare" and plans to build a wall along the U.S.-Mexico border.

His supporters admire Trump's experience in business, including as a real estate developer and reality television star, and view him as an outsider and problem-solver.

About 28,000 security personnel, miles (kilometers) of fencing, roadblocks, street barricades and dump trucks laden with sand will be part of the security cordon clamped around 3 square miles (almost 8 square 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.

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 United States and around the world as well.

An anti-Trump protest also is scheduled for New York on Thursday evening when Mayor Bill de Blasio, filmmaker Michael Moore and actors Mark Ruffalo and Alec Baldwin, who portrays Trump on "Saturday Night Live," take part in a rally outside the Trump International Hotel and Tower.

A major group of protesters, Disrupt J20, has vowed to stage demonstrations at each of 12 security checkpoints and block access to the festivities on the grassy National Mall.

One Washington inaugural protest will come amid a haze of pot smoke as pro-marijuana protesters show their opposition to Trump's choice for attorney general, Alabama Republican Senator Jeff Sessions, a critic of pot legalization.

The group plans to distribute 4,200 joints at the inauguration and urge attendees to light up. Possession of small amounts of marijuana is legal in Washington, but public consumption is not.

Interim Police Chief Peter Newsham said officers were prepared to carry out mass arrests, though authorities hoped that would not be necessary.

"If we do have a mass arrest, we'll be able to get people processed very quickly," he said in an interview with Washington's NBC 4 television station.

Police and security officials have said repeatedly they are committed to guaranteeing 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.

The inaugural parade down Pennsylvania Avenue will pass the

Trump International Hotel, a rallying point for protesters since the election now encircled by security fences.

In a sign of the Trump-related angst gripping Washington, the dean of the Washington National Cathedral said this week its choir would sing "God Bless America" at the inauguration despite misgivings by some members.

"Let me be clear: We are not singing for the President. We are singing for God because that is what church choirs do," the Reverend Randolph Marshall Hollerith said in a letter.

Trump will attend an interfaith prayer service at the cathedral on Saturday which will bring to a close the inaugural ceremonies.