Organisers said they hoped their protest would be one of the biggest in the capital since the Vietnam era, and it was clear they had been careful to create a diverse, inclusive group of speakers. The massive rallies aimed to break legislative gridlock that has long stymied efforts to increase restrictions on firearms sales.

Edna Chavez, 17, from Manual Arts high school in Los Angeles, took the stage with a raised fist and spoke powerfully about her brother, who was killed by gun violence. “I have learned to duck from bullets before I learned to read.” She led the crowd to chant his name, “Ricardo! Ricardo!”

Trevon Bosley, a high school student from Chicago whose brother was killed, said: “I’m here to speak for those youth who fear they may be shot while going to the service station, the movies, the bus stop, to church or even to and from school. I’m here to speak for those Chicago youth who feel their voices have been silenced for far too long.”

Yolanda Renee King, granddaughter of Martin Luther King, told the crowd: “I have a dream that enough is enough. And that this should be a gun-free world, period.”

She then asked the crowd to repeat back her words: “Spread the word, have you heard? All across the nation. We are going to be a great generation.”

She led the chant three times, encouraging the crowd to repeat her words “so the whole world can hear”.

As the students gathered, Donald Trump was whisked by motorcade to his West Palm Beach golf club. Trump later tweeted support for “the victims of the horrible attack in France yesterday” but did not mention the rallies on Twitter. A White House statement read: “We applaud the many courageous young Americans exercising their first amendment rights today. Keeping our children safe is a top priority of the president’s, which is why he urged Congress to pass the Fix NICS and STOP School Violence Acts, and signed them into law.”

The administration also drew attention to reforms the president has called for, including a move by the justice department on Friday to ban bump stocks, the accessory that allows rifles to mimic the rapid fire of automatic weapons.

Veteran civil rights leader John Lewis said the protests reminded him of the early days of the civil rights era. “I think it’s amazing,” he said. “They will be the leaders of the 21st century.”

Watch: What happened outside Florida high school during shooting

In one of the first speeches, Marjory Stoneman Douglas senior Delaney Tarr told the crowd of the students’ demands, including background checks and a ban on assault weapons. “When you give us an inch, that bump stocks ban, we will take a mile,” she said. “We are not here for breadcrumbs, we are here to lead.”

Earlier, The Guardian spoke to Cassie Pearce, 17, who had ridden in her school bus for 10 hours from Manchester, Vermont with dozens of her classmates. Clutching a sign that read “I should be writing my college essay, not my will”, Pearce said: “I’m here because enough is enough. We have a right to be heard. We don’t want to be killed in school.”

In a meeting with lawmakers in the aftermath of Parkland, the president had signalled support for stronger background checks on gun purchases and raising the minimum age for buying high-powered rifles. But the NRA staunchly opposed these measures and Trump appears to have backed off from full-scale checks.

Trump on Friday signed a US$1.3 trillion spending bill including modest improvements to background checks for gun sales and grants to help schools prevent gun violence.

The scenes of thousands of students on the streets was overwhelming to many of the victims of gun violence who attended the Washington rally. “I did not expect this. I’m still astounded,” said Mark Barden, whose seven-year-old son Daniel was one of the 20 children murdered at Sandy Hook in 2012. “To me, it looks like our entire nation is finally on board.”

Barden has spent five years pushing for stricter gun control laws, first with the support of Barack Obama’s White House, then continuing when gun control again dropped off the national agenda.

Former president Obama said on Twitter that he and his wife Michelle were inspired by all the young people who made the marches happen.

“Keep at it. You’re leading us forward. Nothing can stand in the way of millions of voices calling for change,” Obama said.

While the day was focused on the youth, Sir Paul McCartney stood in solidarity with marchers in New York’s Central Park and referred to John Lennon’s fatal shooting outside his block of flats in 1980. “One of my best friends was killed by gun violence right around here, so it’s important to me not just to march today but to take action tomorrow and to have these people to have their voices heard,” he told CNN.

The NRA stayed silent on the student gatherings. However, there were a number of counter protests in some cities.

Outside the FBI headquarters in Washington, about 30 gun-rights supporters staged a quiet counter-demonstration, holding signs reading “Armed victims live longer” and “Stop violating civil rights”.

Associated Press reported that in Salt Lake City, Utah about 500 pro-gun marchers walked to the state Capitol building, where they were far outnumbered by an estimated 15,000 gun control marchers.

While classmates were rallying in Washington, more than 20,000 people – Stoneman Douglas survivors, their families and supporters – gathered in Parkland, Florida, the scene of last month’s shooting. They heard speeches at Pine Trails Park before walking the mile south to the school.

“Parkland is a family. And when our family is hurting, we all come together,” said Liam Kiernan, a 15-year-old Parkland student. “We become stronger because we feel we’re all one person.”

Max Schachter, the father of Alex, a 14-year Stoneman Douglas marching band musician, broke down in tears as he recalled how his son enjoyed playing basketball with his older brother and teaching his little sister “to become a better trombone player”. Schachter said that on 13 February he was like any other parent, wanting his children to be happy and get good grades. Then the Valentine’s Day shooting happened.

“Since the day that changed my life, I will not stop fighting for change,” he said.

Additional reporting by Reuters