US PRESIDENT Donald Trump has described London as “like a war zone” while simultaneously advocating for the US right to bear arms at the National Rifle Association (NRA) convention in Texas.

Describing a hospital in the British capital, the president told the crowd of gun enthusiasts in Dallas that knife crime in the area has become prolific.

“A once very prestigious hospital right in the middle is like a war zone for horrible stabbing wounds.

“They don’t have guns — they have knives. They say it’s as bad as a military war zone hospital. Knives, knives, knives.”

The president also declared that the right to bear arms in the US was “under siege”, however, he assured the tens of thousands of attendees that they had an administration in Washington that was “fighting to protect your Second Amendment”.

He pledged to the cheering crowd that those rights “will never, ever be under siege as long as I’m your president”. Trump did not elaborate on how the Second Amendment was under siege.

The president was addressing the NRA gathering nearly three months after a deadly shooting at a high school in Parkland, Florida. He was speaking at the event for the fourth year in a row.

He temporarily strayed from the group’s strong opposition to tougher gun controls after the school shooting — only to rapidly return to the fold.

Last year, he became the first sitting president to appear in more than 30 years, declaring that the “assault” on the Second Amendment had ended. But this year’s speech in Dallas came as the issue of gun violence takes on new urgency after one of the deadliest school shootings in US history.

Survivors of the February 14 shooting at Marjory Stoneman Douglas High School that left 17 people dead are leading a massive national gun control movement.

Several groups have announced plans to protest over the weekend during the NRA event. The protesters will include parents of those killed in Parkland and other shootings.

The survivors’ campaign has not led to major changes from the White House or the Republican-led Congress but Trump did briefly declare he would stand up to the powerful gun lobby.

He later back-pedalled, expressing support for modest changes to the background check system, as well as arming teachers.

His attendance at this year’s NRA convention was announced just days ago and came after Vice President Mike Pence was already scheduled to appear.

Asked why Trump was attending, given political tensions around gun violence, White House press secretary Sarah Huckabee Sanders said this week that safety was a “big priority”.

“We also support the Second Amendment, and strongly support it, and don’t see there to be a problem with speaking at the National Rifle Association’s meeting,” she said.

Trump has long enjoyed strong backing from the NRA, which spent about US$30 million ($40 million) supporting his presidential campaign.