Beto O'Rourke Backs U.S. Assault Weapons Ban

Beto O'Rourke has invoked a school shooting last year near Houston to call for banning assault weapons and points to that city's 2017 devastation during Hurricane Harvey to push for fighting climate change.

The former Democratic congressman is formally launching his presidential campaign with Saturday rallies across Texas.

He began in his native El Paso, then visited Houston's historically black Texas Southern University and is holding a late-night Austin event.

Wearing a Texas Southern cap, O'Rourke recalled the deadly shooting at Santa Fe High School last May. He advocated for universal background checks for firearms purchases.

O'Rourke also said he wanted to ensure that weapons "sold to the United States military with the sole purpose of killing people" are confined to the battlefield.

He said Harvey meant Houston understands the perils climate change "better than just about anyone."

Democratic presidential candidate Beto O'Rourke makes a speech in El Paso, Texas. Image: AAP

O'Rourke has told 1000-plus supporters near the Texas-Mexico border that immigrants make the country stronger.

He offered support for unapologetically liberal positions, including backing federal legalisation of marijuana. He promised to strengthen unions nationwide, make it easier to register to vote and end the war in Afghanistan.