Democrats staged a "sit-in" on the floor of the U.S. House of Representatives on Wednesday demanding the chamber remain in session until Republicans agree to a vote on gun control legislation following the Orlando mass shooting.

Chanting "No bill, no break!" scores of Democratic lawmakers joined in the protest that began around midday and continued well into the evening even as House Republican leaders sought to maneuver around the Democrats' sit-in by using procedural rules to schedule a vote on unrelated legislation.

Democrats vowed to continue their demonstration.

"We are in for the long haul here," House Democratic leader Nancy Pelosi told reporters, saying members intended to keep up their sit-in as long as it takes to get a vote on a bill.

But Republican House Speaker Paul Ryan said he would not bend to the Democrats' demands, which he called a "publicity stunt" and vowed not to bring up any bill that would take away gun owners' constitutional rights.

Not since August 2008, when House Republicans, then in the minority, took the floor to demand a vote on allowing offshore drilling has the House been brought to a standstill by a protest.

The Democrats' move echoed last week's filibuster by Senate Democrats to protest inaction on guns in the wake of the June 12 massacre at a gay nightclub in Orlando, Florida, where a gunman killed 49 people and wounded 53 in the deadliest mass shooting in modern U.S. history.

After the Senate talk-a-thon, the Senate's Republican majority scheduled votes on four gun control measures - all of which failed on Monday. Work on a compromise is under way.

Guns are a potent U.S. political issue and Americans are on edge after mass shootings in recent years in Connecticut, Colorado, California and elsewhere. Congress has not passed major gun control legislation since 1994, with gun rights defenders saying such measures infringe on the constitutional right to bear arms.

Ryan said he would not follow suit: "They know that we will not bring a bill that takes away a person's constitutionally guaranteed rights without ... due process," he said on CNN.

Instead, Republicans said on Wednesday evening they would reconvene to vote on financial regulation legislation and file a $1.1 billion funding measure to fight Zika in a move aimed at returning the chamber to order.

CHANTING LAWMAKERS

But the Democratic protesters stayed in the chamber into the evening giving impassioned speeches and urging action before a break scheduled to begin this weekend through July 5, vowing to stay all night beyond any votes.

Led by Representative John Lewis, a Democrat from Georgia and veteran of the 1960s civil rights movement, Democrats urged gun control measures such as tighter background checks and legislation to curb the sale of weapons to people on government watch lists.

More than eight hours into the sit-in, Lewis gave an impassioned speech on the House floor to the more than 100 fellow Democrats huddled around him urging them to "never, ever give up."

"They (the American public) want us to do something. We have a moral obligation, a mission and a mandate to do something," Lewis said to applause and cheering.

Pelosi invoked not only Orlando but other mass shootings including the attack a year ago by a white man at a black church in Charleston, South Carolina, that killed nine. “Right now there is an opportunity," she said.

Earlier on Wednesday, the House's presiding officer, Republican Representative Ted Poe, entered the chamber around noon (1600 GMT) to find a number of Democratic lawmakers in the front of the chamber chanting, some sitting on the floor.

After banging the gavel in an attempt to clear the protesters, he announced the chamber would be in recess and left.

Several Democratic senators crossed the Capitol to join protesters, including Senators Elizabeth Warren, Tim Kaine and Cory Booker, all mentioned as potential running mates for presumptive Democratic presidential nominee Hillary Clinton. Clinton's rival in the Democratic race, Senator Bernie Sanders, also appeared.

Tweets of support came from outside Congress. "Thank you John Lewis for leading on gun violence where we need it most," President Barack Obama tweeted.

Clinton tweeted: "This is what real leadership looks like."

Lawmakers also took to social media to document their demonstration with video and pictures, particularly after House Republicans shut down video cameras that normally document the chamber.

Outside the Capitol, nearly 50 people gathered in solidarity at a rally organized by Everytown for Gun Safety, the advocacy group backed by former New York Mayor Bloomberg.

Many House Republicans said they viewed the problem differently from Democrats. "We don't view the fact that someone becomes radicalized and decides to kill a bunch of Americans ... as a gun problem," Representative John Fleming of Louisiana said on Wednesday. "We view that as a terrorist problem."