A former US congresswoman who was shot in the head in a 2011 mass shooting begged lawmakers at an emotional hearing to act quickly to curb firearms because "US citizens are counting on you". Not everyone agreed, underscoring the national political divide over gun control.

Giffords' 80-word plea was Wednesday's most riveting moment, delivered in a hushed, halting voice two years after the Arizona Democrat suffered head wounds in a Tucson shooting spree that killed six people. The session came two months after 20 children and six women were slain by a gunman who invaded Sandy Hook Elementary School in Newtown, Connecticut.

Shooting victim and former US congresswoman Gabby Giffords and her husband, retired NASA astronaut Mark Kelly, prepare to give an opening statement before the Senate Judiciary Committee during a hearing on gun control on Capitol Hill in Washington on Wednesday. [Photo/Agencies]

At the same hearing, a top official of the nation's most powerful gun lobby group, the National Rifle Association, rejected Democratic proposals to ban assault weapons and high-capacity ammunition magazines and said requiring background checks for all gun purchases would be ineffective because the Obama administration is not doing enough to enforce the law as it is.

Even if stronger background checks did identify a criminal, "as long as you let him go, you're not keeping him from getting a gun and you're not preventing him from getting to the next crime scene", said Wayne LaPierre, the NRA's executive vice-president.

Giffords, who retired from Congress last year, focused during her brief appearance on the carnage from armed assailants.

"Too many children are dying," she said at the Senate Judiciary Committee hearing.

Guiding her in and remaining to testify, was Mark Kelly, the retired astronaut who is Giffords' husband. The couple, who both own guns, have formed a political action committee called Americans for Responsible Solutions that backs lawmakers who support gun restrictions.

"We're simply two reasonable US citizens who realize we have a problem with gun violence and we need Congress to act," Kelly said.

The hearing kicked off a year in which US President Barack Obama and members of Congress are promising to make gun restrictions a top priority. Obama has already proposed requiring background checks for all gun sales and reviving both an assault weapons ban.

Republican Senator Ted Cruz joined others in lauding Giffords but expressed little interest in curbing firearms.

"Unfortunately in Washington, emotion I think often leads to bad policies," said Cruz. He said gun control efforts too often "restrain the liberties of law-abiding citizens", not criminals.

Republicans blamed the nation's gun troubles on a list of maladies including a lack of civility, violent video games and insufficient attention to people with mental problems. Senator Charles Grassley, top Republican on the panel, said that while he welcomed the renewed focus on guns, "The deaths in Newtown should not be used to put forward any gun control proposal that's been floating around for years."