US President Joe Biden renewed his call Sunday for Congress to ban semi-automatic rifles like the one used in a weekend shooting that left eight victims including children dead in Texas, as he called out Republican inaction.

The president ordered US flags lowered to half staff one day after a heavily-armed gunman opened fire without warning at an outlet mall north of Dallas, in the latest spasm of gun violence to shake the nation.

"Once again I ask Congress to send me a bill banning assault weapons and high-capacity magazines. Enacting universal background checks. Requiring safe storage. Ending immunity for gun manufacturers," Biden, for years a proponent of tougher gun laws, said in a statement.

"I will sign it immediately. We need nothing less to keep our streets safe."

Witnesses and police described scenes of panic and horror at the Allen Premium Outlets, where video footage circulating online showed the shooter getting out of a sedan and opening fire on people walking nearby.

The president said he and First Lady Jill Biden were praying for the victims and their families and were "grateful to the first responders who acted quickly and courageously to save lives."

But an exasperated Biden also pointed to the staggering number of mass shootings this year, already nearly 200, and the more than 14,000 firearm deaths, noting that the leading cause of death for American children is gun violence.

"Too many families have empty chairs at their dinner tables," he went on. "Republican members of Congress cannot continue to meet this epidemic with a shrug. Tweeted thoughts and prayers are not enough."

The stinging rebuke refers to the typical responses from lawmakers in the aftermath of such violence.

Republicans in particular have been accused of offering "thoughts and prayers," but little concrete action to reduce gun deaths.

Biden, after several recent mass shootings, has called for reinstating the assault weapons ban that he helped pass through Congress in 1994 when he was a senator, but which lapsed in 2004.

Getting such a bill through today's divided Congress appears all but impossible, with the vast majority of Republicans opposed to such restrictions.