Students across the US have streamed out of their schools in the latest round of gun control protests following the February shooting at a high school in Parkland, Florida.
The protests were chosen to line up with the 19th anniversary of the Columbine High School shooting, which left 13 people dead in Littleton, Colorado.
At 10am in each time zone, students at dozens of schools left class to take moments of silence honouring the victims at Columbine and other shootings.
From there, some students headed to rallies at their statehouses. Others stayed at school to discuss gun violence. Some are holding voting registration drives.
Hundreds of Washington-area students gathered at a park near the White House, taking 19 minutes of silence for each year that has passed since the Columbine massacre. In New York City, crowds of students gathered in Washington Square Park and lay down in a "die-in".
Organizers say there will be walkouts in every state, with more than 2,700 registered on the event's website.
City-wide protests are expected to attract thousands in New York City and Austin, Texas. Police in Richmond, Virginia, say they expect at least 10,000 at the state Capitol.
Shortly before the walkouts, another school shooting in Florida left one student injured. Authorities say one student shot another in the ankle at Forest High School in Ocala. A suspect was taken into custody.
At Marjory Stoneman Douglas High School, where a gunman killed 17 on February 14, student David Hogg said the latest shooting underscored the urgency of the protests.
"We have to stop this. We're not going to be able to stop this unless we continue to make our voices heard, though, when our elected officials won't," David said in a video posted to social media. "We have to get out there and make our voices heard, not as Democrats or Republicans, but as Americans."
David was among about 50 students who walked out of Stoneman Douglas after administrators threatened protesters with unexcused absences.
Craig Smith and Terry McGary, both 17-year-old juniors, said they walked out because they want to show respect for the Columbine victims.
"It was a guilt trip to make us not walk out," Terry said about the threat.
Craig said gun violence can "no longer be swept under the covers".
"This is the only way to bring attention to the issue," he said.
The walkouts are the latest in a wave of youth activism that has emerged after the Parkland massacre.
Tens of thousands of students left class on March 14 to protest against gun violence in what historians called the largest youth protest movement since at least the Vietnam War. Days later, hundreds of thousands of teens and their backers rallied across the US calling for tougher laws on guns and ammunition.
Plans for Friday's walkout began only hours after the Parkland shooting, when a Connecticut teenager started an online petition calling for protests on the anniversary of Columbine. Sophomore Lane Murdock then gathered a few other students at Ridgefield High School to orchestrate the national protest.
They also have received help from Indivisible, a left-leaning nonprofit based in Washington that helps boost grassroots activism. The group says it was formed after the 2016 election to oppose the policies promoted by President Donald Trump.
"We're walking out to remember every single young person who has been killed by American gun violence," Lane said in a statement on Thursday. "We're walking out to talk about the real problems our country is facing, and the solutions that our leaders are too scared to dream up."