Columbine. Newtown. And now, Parkland.

A grim fellowship of parents, teachers and students affected by school shootings over the past two decades sat down with US President Donald Trump as the White House sought to show resolve against gun violence amid questions about the president's commitment to action.

A strong supporter of gun rights, Trump has nonetheless indicated in recent days that he was willing to consider ideas not in keeping with National Rifle Association orthodoxy, included age restrictions for buying assault-type weapons.

The president is facing growing calls for action on gun control after the mass shooting that took 17 lives at Marjory Stoneman Douglas High School in South Florida.

Still, while Trump said he wants to listen and has offered support for some limited gun-control measures, gun owners are a key part of his base.

The NRA did not respond to a request for comment. Trump embraced gun rights on his campaign, though he supported some gun control before he became a candidate, backing an assault weapons ban and a longer waiting period to purchase a gun in a 2000 book.

Throughout the day Wednesday, television news showed footage of student survivors of the violence marching on the Florida state Capitol, calling for tougher laws. The protests came closer to Trump, too, with hundreds of students from suburban Maryland attending a rally at the Capitol and then marching to the White House.

Alfonso Calderon, who survived the Parkland, Florida, school shooting, says he and fellow students aren't being taken seriously enough in their calls for gun reform.

On Tuesday, Trump directed the Justice Department to move to ban devices like the rapid-fire bump stocks used in last year's Las Vegas massacre. The White House also said Trump was looking at a bill that would strengthen federal gun background checks.

But those moves have drawn criticism as being inadequate, with Democrats questioning whether the Justice Department even has authority to regulate bump stocks and arguing that the background check legislation would not go far enough.

The Justice Department did not immediately respond to requests for comment about how it might implement Trump's order or how an ongoing bump stock review would be affected.

As calls for ATF to ban bump stocks mounted after the Las Vegas shooting, the agency initially said it could only reconsider their lawfulness if Congress amended existing laws or passed new legislation. An effort to pass legislation last year fizzled out.

On background checks, Trump suggested he was open to a bipartisan bill developed in response to a mass shooting at a Texas church. It would penalise federal agencies that don't properly report required records and reward states that comply by providing them with federal grant preferences.

Senate Minority Leader Chuck Schumer, a New York Democrat, said the bill is "a small step," stressing that Democrats want to see universal background check legislation.

Republican Sen. Pat Toomey of Pennsylvania said Wednesday that he'll probably reintroduce bipartisan legislation that would require background checks for all gun purchases online and at gun shows. He said he planned to discuss the idea with Trump.

That bill first emerged with backing from Toomey and Democratic Sen. Joe Manchin of West Virginia following the 2012 slaying of 26 children and adults in Connecticut's Sandy Hook Elementary School. It failed then and at least one more time since.