Hundreds of thousands have massed for a “Women’s March on Washington”, part of a global day of protests against new US President Donald Trump.
The rally is one of more than 600 being held worldwide on the president’s first full day in office.
The aim is to highlight women’s rights, which protesters believe to be under threat from the new administration.
Mr Trump attended a multi-faith service at Washington National Cathedral and is visiting the CIA HQ in the afternoon.
He has taken his first steps as president, signing an executive order targeting his predecessor’s health care scheme.
Protesters swarmed the streets and metro stations of the US capital on Saturday as they headed to the National Mall to hear speeches.
Organisers had originally sought a permit for 200,000 people but say they now expect as many as half a million, possibly dwarfing Friday’s inauguration crowd, the Washington Post reported.
A planned march to the White House is now in doubt as the entire route is filled with demonstrators. Interim DC Police Chief Peter Newsham told Associated Press: “The crowd stretches so far that there’s no room left to march.”
Celebrities such as Katy Perry, Scarlett Johansson, Amy Schumer, Ugly Betty star America Ferrera, Patricia Arquette and Michael Moore are said to be attending.
But there are other protests in some 300 cities across the US, from New York to Seattle. The scale of the turnout in Chicago prompted police to designate it a rally rather than a march.
Organisers of a London rally said between 80,000 and 100,000 people had taken part there.
During his speech in Washington, Michael Moore ripped up a copy of the Washington Post, saying: “The headline was ‘Trump takes power’. I don’t think so. Here’s the power. Here’s the majority of America right here. We are the majority.”
The singer Madonna also made an appearance, swearing several times in a speech carried live by major US TV networks.
“Yes I am outraged. Yes, I have thought an awful lot about blowing up the White House,” she said.
Many women have knitted pink “pussy hats” – a reference to a recording that emerged during the election campaign in which Mr Trump talked about groping women.
Placards in Washington read: “Women won’t back down”, “Walls will not divide us” and “Less fear more love”.
Defeated presidential candidate Hillary Clinton sent a tweet of support.
Organisers of the Women’s March on Washington said in a statement: “The rhetoric of the past election cycle has insulted, demonised, and threatened many of us.
“The women’s march on Washington will send a bold message to our new government on their first day in office, and to the world that women’s rights are human rights.”
They said the protest would not simply be about women’s rights and would attract “people of all genders, ages, races, cultures, political affiliations and backgrounds”, with support from the likes of Amnesty International.
The rally is peaceful, easing fears of a repeat of the violence that occurred after the inauguration ceremony on Friday, when protesters smashed windows. More than 200 were arrested and six officers hurt.
‘These are global problems’
Anti-Trump marches have already taken place in Australia, New Zealand and in Asian cities such as Bangkok.
Several thousand women and men joined a rally in central Sydney, with a similar number in Melbourne.
Women’s March Sydney co-founder Mindy Freiband told the crowd there: “Hatred, hate speech, bigotry, discrimination, prejudicial policies – these are not American problems, these are global problems.”
American expatriate Bill Scholer, protesting in Tokyo, told Reuters news agency: “Everything we value could be gone. It’s time to speak your mind and concerns and to do our best to salvage the values we cherish in America.”
London, Belfast, Cardiff, Edinburgh, Leeds, Liverpool, Manchester and Bristol were among the UK cities holding protests, while Barcelona, Rome, Amsterdam, Geneva, Budapest, Prague and Berlin were among the European cities.
Mr Trump’s Washington National Cathedral service was scheduled to be his sole official engagement on Saturday, although it has now been announced he is visiting the CIA HQ in Langley, Virginia, in the afternoon.
Mr Trump has been critical of intelligence services, but his spokesman Sean Spicer tweeted: “Excited to thank the men and women of the intelligence community.”
Mr Trump has already ordered agencies to ease the “economic burden” of the health laws known as Obamacare. His team also quickly overhauled the White House website.
The website revamp replaces Barack Obama’s policies with Mr Trump’s new agenda.
The new administration lists only six issues on the website – energy, foreign policy, jobs and growth, military, law enforcement and trade deals.
Critics point out that it makes no mention of civil rights, LGBT rights, healthcare or climate change.
In Friday’s inaugural address, Mr Trump pledged: “From this moment on, it’s going to be America First. We will follow two simple rules: Buy American and hire American.
“Every decision on trade, on taxes, on immigration, on foreign affairs, will be made to benefit American workers and American families.”