US President Donald Trump has called for immediate and significant changes to the nation's gun laws while criticising American legislators for being "petrified" of the politically powerful National Rifle Association (NRA) lobby.

Trump held a televised meeting with lawmakers at the White House that stretched for an hour on Wednesday, and he rejected both his Republican party's incremental approach and its strategy on gun legislation.

Giving hope to Democrats, he said he favoured a "comprehensive" approach to addressing violence such as the recent deadly shooting at a Florida high school, although he offered no details.

"We can't wait and play games, and nothing gets done," Trump said as he opened the session with 17 House and Senate lawmakers. "We want to stop the problems."

Democratic legislators made a point of appealing to the president to use his political power to persuade his party to take action. "It is going to have to be you," Senator Chris Murphy told Trump.

The president's call for stronger background checks - which are popular among Americans - has been resisted by Republicans in Congress and the NRA.

Republicans have instead been leaning towards modest legislation designed to improve the background system already in place.

'Take the guns first'

Trump made clear he was looking for more, and accused lawmakers of being "petrified" of the gun lobby, adding he told NRA officials it's time to act.

"We have to stop this nonsense," the president said.

Trump raised eyebrows by suggesting law enforcement officials should be able to confiscate people's firearms without a court order to prevent potential tragedies.

"Take the guns first, go through due process second," he suggested.

Democrats said they were concerned Trump's interest may fade quickly. After the meeting, Murphy told reporters: "I'm worried that this was the beginning and the end of the president's advocacy on this issue. The White House has to put some meat on the bones. The White House has to send a proposal to Congress."

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Among those at the meeting was Senator Pat Toomey who is pushing a bill to broaden background checks. Trump asked Toomey if his plan to expand such checks included raising the minimum age for young people to buy an assault weapon. It is currently 18 years old.

Toomey told the president it did not.

"You know why," Trump scoffed. "Because you're afraid of the NRA."

Toomey said on Thursday he didn't fear the NRA, and he called on Trump to back his measure, believing it has a better chance of passing now.