"If you listen real close, you can hear the people in power shaking," David Hogg, a survivor of the Florida school shooting who has emerged as one of the student leaders of the movement, told the roaring crowd of demonstrators at the March for Our Lives rally in Washington.
He warned: "We will get rid of these public servants who only care about the gun lobby."
Chanting "Vote them out!" and bearing signs reading "We Are the Change", "No More Silence" and "Keep NRA Money Out Of Politics", the protesters packed Pennsylvania Avenue between the Capitol and the White House.
Large rallies with crowds estimated in the tens of thousands in many cases also unfolded in such cities as Boston, New York, Los Angeles, Chicago, Houston, Fort Worth, Minneapolis, and Parkland, Florida, the site of the February 14 attack at Marjory Stoneman Douglas High School that left 17 people dead.
Emma Gonzalez, survivor of the Florida school shooting delivered a powerful speech at the Washington DC rally.
“In a little over six minutes, 17 of our friends were taken from us,” González said at the beginning of her speech. “Everyone who was there understands. Everyone who has been touched by the cold grip of gun violence understands.”
“For us, long, tearful, chaotic hours in the scorching in the afternoon sun were spent not knowing,” she continued. “No one could understand the extent of what had happened. No one could believe that there were bodies in that building waiting to be identified for over a day.”
“For those who still can’t comprehend because they refuse to, I’ll tell you where it went: right into the ground, six feet deep,” González said before listing the names of her slain friends.
Protesters denounced the National Rifle Association and its allies and complained that they are scared of getting shot in school and tired of inaction by grown-ups after one mass shooting after another.
They called for such measures as a ban on high-capacity magazines and assault-type rifles like the one used by the Florida killer, tighter background checks and school security, and a raising of the age to buy guns.
"I'm really tired of being afraid at school," said Maya McEntyre, a 15-year-old high school freshman from Northville, Michigan, who joined a march by thousands in Detroit.
"When I come to school, I don't want to have to look for the nearest exit."
She added: "I want to get to the problem before it gets to me."
Sister demonstrations took place worldwide in cities such as Dublin, London, Edinburgh, Paris and Sydney. In Dublin, protesters gathered outside the US Embassy in Ballsbridge to show their support.
In Atlanta, Ben Stewart, a 17-year-old senior at Shiloh Hills Christian School in Kennesaw, Georgia, took part in a march in Atlanta to press for what he called "common-sense gun laws".
"People have been dying since 1999 in Columbine and nothing has changed. People are still dying," he said. "It could be prevented."
Celebrities including Miley Cyrus, Kim Kardashian, Kanye West, Demi Lovato, Amy Schumer, Ariana Grande and Olivia Wilde joined the anticipated one million people protesting across the US.
Cyrus who is due to perform at the Washington DC rally - shared photos of her and her family on social media as she vowed: "I won't ever give up & neither will the millions that march with us today! #EndGunViolence."
Donald Trump was in Florida for the weekend. A motorcade took him to his West Palm Beach golf club on Saturday morning. As of early afternoon, he had yet to weigh in on Twitter about the protests.
The National Rifle Association went silent on Twitter in the morning, in contrast to its reaction to the nationwide school walkouts against gun violence March 14, when it tweeted a photo of an assault rifle and the message "I'll control my own guns, thank you".
About 30 gun-rights supporters staged a counter-demonstration in front of FBI headquarters in Washington, standing quietly with signs such as "Armed Victims Live Longer" and "Stop Violating Civil Rights".
Organisers of the gun-control rally in the nation's capital hoped their protest would match in numbers and spirit last year's women's march, which far exceeded predictions of 300,000 demonstrators.
"We will continue to fight for our dead friends," Delaney Tarr, another survivor of the Florida tragedy, declared from the stage. The crowd roared with approval as she laid down the students' central demand: a ban on "weapons of war" for all but warriors.
The Reverend Martin Luther King Jr's nine-year-old granddaughter Yolanda Renee King gave a rousing speech at the Washington rally, drawing from the civil rights leader's most famous words.
"I have a dream that enough is enough," she said. "That this should be a gun-free world. Period."
In Parkland, the police presence was heavy as more than 20,000 people filled a park near the school, chanting slogans such as "Enough is enough" and carrying signs that read "Why do your guns matter more than our lives?" and "Our ballots will stop bullets".
Gun violence was also fresh for some in the Washington crowd: Ayanne Johnson of Great Mills High in Maryland held a sign declaring, "I March for Jaelynn," honouring Jaelynn Willey, who died on Thursday, two days after being shot by a classmate at the school. The classmate also died.
Rallying outside the New Hampshire Statehouse in Concord, 17-year-old Leeza Richter said: "Our government will do more to stop us from walking out than it will to stop a gunman from walking in."
Since the bloodshed in Florida, students have tapped into a current of gun control sentiment that has been building for years - yet still faces a powerful foe in the NRA and its supporters.
Organisers hope the passions of the crowds and the under-18 roster of speakers will translate into a tipping point starting with the midterm congressional elections this fall.
In addition to pushing for tighter gun laws, the students have been working to register young people to vote.
Polls indicate public opinion in the US may be shifting on the issue.
Polls indicate that public opinion nationwide may indeed be shifting on an issue that has simmered for generations, and through dozens of mass shootings.
A new poll conducted by The Associated Press-NORC Centre for Public Affairs Research found that 69% of Americans think gun laws in the United States should be tightened.
That was up from 61pc who said the same in October of 2016 and 55pc when the AP first asked the question in October of 2013. Overall, 90pc of Democrats, 50pc of Republicans and 54pc of gun owners now favour stricter gun control laws.
But even with claims of historic social momentum on the issue of gun control, the AP poll also found that nearly half of Americans do not expect elected officials to take action. Among the questions facing march organisers and participants will be how to translate this one-day event, regardless of turnout, into meaningful legislative change.
One way is by channelling the current energy into the midterm congressional elections this autumn.
Students in Florida have focused on youth voter registration and there will be a registration booth at the Saturday rally.
Press Association