The day, sponsored by the United Nations since 1975, celebrates women's achievements and aims to further their rights. U.N. Secretary-General Antonio Guterres told a commemoration at U.N. headquarters in New York that "remarkable progress on women's rights and leadership" in recent decades has sparked a backlash from "an entrenched patriarchy."
And he warned that "nationalist, populist and austerity agendas add to inequality with policies that curtail women's rights and cut social services." "I do not accept a world that tells my granddaughters that economic equality can wait for their granddaughter's granddaughters," Guterres said. "I call for a new vision of equality and opportunity so that half the world's population can contribute to all the world's success."
Millions of others around the world demanded equality amid a persistent salary gap, violence and widespread inequality.
Police in the Ukrainian capital Kiev detained three people as far-right demonstrators tried to provoke activists protesting domestic and sexual violence.
About 300 people gathered on Mykhailivska Square in central Kiev on Friday for the women's rights demonstration. Several dozen far-right demonstrators stood nearby, holding placards reading "God! Homeland! Patriarchy!" and "Feminism is destroying Ukrainian families."
In Spain, where women's rights have become one of the hot topics in the run-up to a general election next month, many female employees didn't show up to work Friday. Others also halted domestic work or left to men the care of children and ill or elderly people.
In the evening, cities across the country lit landmark buildings with purple lights as hundreds of thousands poured into the streets.
"We are getting killed and we are getting lower salaries for being women, but that's just the tip of the iceberg," said Sara Baladron, a 27-year-old pharmacist joining the protest in central Madrid.
In neighboring Portugal, the Cabinet observed a minute of silence Thursday as part of a day of national mourning it decreed for victims of domestic violence. Portuguese police say 12 women have died this year in domestic violence incidents — the highest number over the same period in 10 years.
Pope Francis hailed the "irreplaceable contribution of women" to fostering peace.
"Women make the world beautiful, they protect it and keep it alive," the Argentine Jesuit said.
Francis has vowed to give more decision-making roles to women in the Catholic Church, where the priesthood —and therefore the highest ranks of authority— is reserved for men. Some feminists bristle at Francis' frequent use of the term "feminine genius" and his focus on women as mothers.
In Germany, topless feminist protesters went to one of the country's most famous red-light districts in Hamburg and pulled down a metal barrier wall intended to keep out women — other than prostitutes.
A half-dozen women belonging to the Femen activist group had the slogan "No brothels for women" written on their bare back in black lettering.
Legally, all women are allowed to enter the street, but in reality most women obey the signs saying, "Entry only for men 18+."
In France, the first Simone Veil prize went Friday to a Cameroonian activist who has worked against forced marriages and other violence against girls and women. Aissa Doumara Ngatansou was married against her will at age 15 but insisted upon continuing her studies as a young wife. She has since turned her attention to victims of Boko Haram extremists.
The French award is named for the trailblazing French politician and Holocaust survivor Veil, who spearheaded the fight to legalize abortion.
Meanwhile in Russia, International Women's Day is a public holiday but it mostly lauds gender roles that are now outdated. As is his custom every year, President Vladimir Putin gave a speech thanking women for their patience, good grace and support.
"You manage to do everything: both at work and at home and at the same time you remain beautiful, charismatic, charming, the center of gravity for the whole family, uniting it with your love," Putin said.
Women in Argentina took to the streets by the tens of thousands, galvanized by the rejection last year of a bill that would have legalized abortion. They marched from Congress to the country's historic Plaza de Mayo square, many carrying signs in support of abortion or with slogans like "my body doesn't want your opinion."
Rallies against violence against women in Argentina, held under the slogan "Not One Less," have drawn multitudes in the past.
"We have achieved a change of era. Sexist violence is no longer accepted, abuses are not accepted, neither is street harassment ... there are many things that have changed," said Marta Dillon, an activist and one of the founders of the "Not One Less" movement.
In Puerto Rico, hundreds clad in purple T-shirts protested to demand safer housing as the U.S. territory struggles to recover from Hurricane Maria, while others held up signs with the names of more than 20 women reportedly killed by their partners on the island last year.
Amid the protests, Gov. Ricardo Rossello signed an executive order that would in part create a special agency to intervene in domestic violence cases and establish preventive police patrols around the homes and workplaces of women awarded protection orders.
Meanwhile, similar scenes played out in other South American countries.
In Brazil, thousands of marchers in Rio de Janeiro targeted far-right President Jair Bolsonaro, who has offended many women with his comments, as well as the country's record of violence against women.
"This year it is especially important to be here because we have a macho president," said 46-year-old psychologist Juliana Lopez. "Brazil is champion in femicides. We must be on the street to be respected. "
Hundreds of women in Bolivia rallied in main cities, carrying giant undergarments bearing messages such as, "underwear of an irresponsible and abusive father" and "underwear of a child molester," as Chilean women also demanded access to free and safe abortions.
And in nearby Ecuador, President Lenin Moreno took the day to announce the creation of a bonus of about $300 per month for the children of victims of femicides.
The bonus will help an estimated 88 orphans.
In India, hundreds of women marched on the streets of New Delhi demanding an end to domestic violence, sexual attacks and discrimination in jobs.
Boys are prized more than girls in India. Thousands of Indian women are killed — often doused in gasoline and burned to death — every year because the groom or his family feel the dowry of the bride is inadequate.
Political parties in India have for years been promising 33 percent of seats for women in the country's Parliament, but they have yet to enact legislation to that effect.
In Indonesia's capital Jakarta, several hundred men and women carried colorful placards calling for an end to discriminative practices such as the termination of employment for pregnancy and exploitative work contracts.
"Our action today is to urge (the government) for our right to a society that's democratic, prosperous, equal and free from violence," said Dian Trisnanti, a labor activist. Girls and women in Indonesia, the world's fourth most populous country, have equal access to education but face higher unemployment, lower wages and poorer working conditions than men.
Both Koreas marked the day. In the South, women wearing black cloaks and pointed hats marched against what they describe as a "witch hunt" of feminists in a deeply conservative society.
College student Noh Seo-young said that South Korea struggles to accept that women are "also humans" and that women have to fight until they can "walk around safely."
In the North, where Women's Day is one of the few national holidays that is not explicitly political in nature, people dressed up for family photo shoots or bought roses for their mothers or wives at the many small, bright orange street stalls in central Pyongyang that sell flowers.
U.S. President Donald Trump honored International Women's Day with a presidential message, saying that the U.S. celebrates women's "vision, leadership, and courage," and reaffirms its "commitment to promoting equal opportunity for women everywhere."
On the eve prior, U.S. first lady Melania Trump saluted women from 10 countries for their courage. The recipients of the International Women of Courage Award included human rights activists, police officers and an investigative journalist.
"Courage is what divides those who only talk about change from those who actually act to change," Mrs. Trump said at a ceremony Thursday that was also attended by Secretary of State Mike Pompeo.
Pompeo separately recognized women in Iran for protesting the requirement that they wear a head covering known as a hijab in public and a Ukrainian activist who died in 2018 after she was attacked with sulfuric acid.
Ethiopian Prime Minister Abiy Ahmed, who named one of the world's few "gender-balanced" Cabinets last year, told a gathering that "women are the pillars of the nation and the least recognized for their sacrifices."
In Nigeria, the U.S. Embassy hosted talks on sexual harassment that included a founder of the recent #ArewaMeToo campaign among women in the country's conservative, largely Muslim north. And in Niger, first lady Aissata Issoufou Mahamadou oversaw the awards in the Miss Intellect Niger contest.
Women protested against gender-based violence in Kenya's capital.
"We haven't gotten to a stage where women are comfortable to come out and say, 'I was sexually abused,'" said protester Esther Passaris. "So what we need to do is slowly, slowly grow."
AP reporters across the globe contributed to this report. Barry Hatton reported from Lisbon, Portugal.