Giffords Kelly
Former US representative Gabrielle Giffords with her husband at a senate judiciary committee hearing on gun violence (Reuters)

Former US congresswoman Gabrielle Giffords, who was shot in the head by a gunman in 2011, opened Senate hearings on gun violence with an emotional plea for tougher regulations.

Giffords, a Democrat and a gun owner, was shot during an attack on a constituency meeting in Tucson, Arizona. Six people died in the assault.

"Speaking is difficult. But I need to say something important," Giffords told the committee assessing the viability of new gun control measures after the massacre of 20 children at Sandy Hook Elementary School in Newtown, Connecticut, in December.

"Violence is a big problem," she said. "Too many children are dying. Too many children.

"We must do something. It will be hard. But the time is now. You must act. Be bold. Be courageous. Americans are counting on you."

Giffords was accompanied by her husband, an astronaut, who was also called as a witness by the Senate judiciary committee.

"We are simply two reasonable Americans who have said 'Enough'," Kelly said, after describing how his wife's attacker fired 33 bullets in 15 seconds before he was stopped while trying to reload his weapon.

The couple has formed a political action committee, to support tighter gun laws and back President Obama on the issue.

When dangerous people get guns

He has proposed a package of measures that includes banning military-style assault weapons, requiring background checks on all firearms purchases and limiting ammunition magazines to 10 rounds.

"When dangerous people get guns we are all vulnerable - at the movies, at church, conducting our everyday business, meeting a government official," Kelly said.

The National Rifle Association (NRA) took the stand before the committee to defend the constitutional right for Americans to bear arms.

"Law-abiding gun owners will not accept blame for the acts of violence of deranged criminals. Nor do we believe the government should dictate what we can lawfully own and use to protect our families," said NRA executive vice-president Wayne LaPierre.

"And when it comes to background checks, let's be honest - background checks will never be universal because criminals will never submit to them.

"Proposing more gun control laws, while failing to enforce the thousands we already have, is not a serious solution to reducing crime," said LaPierre.

He maintained thatv the implementation of stronger school security measures could go some way towards curbing shootings.

In the aftermath of the Sandy Hook shooting, an NRA proposal to arm teachers sparked controversy.

The US has the world's highest proportion of gun ownership.

NRA ceo Wayne LaPierre
Wayne LaPierre, CEO of the National Rifle Association, is sworn in during a hearing before the US Senate (Reuters)